diff --git a/CHANGES.md b/CHANGES.md
index da69d97..df70a5f 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,8 +2,32 @@
 
 ## 0.6.5 (unreleased)
 
+- Fix: SVG (skip-Thumbor) images no longer emit uid-based scale URLs that
+  permanently 404. Root cause was not `purge_scales` but the volatile
+  `ThumborScaleStorage` introduced in 0.6.x: `get_or_generate` reads a
+  fresh empty per-instance dict on every traversal, so *no* uid scale URL
+  could ever resolve — the `plone.scale` annotation is never consulted.
+  Fixed on both ends: skip-types now emit the original field URL with a
+  modification-time cache buster (both plone.namedfile code paths, the
+  legacy `__init__` for 7.x and `_scale_url` for >= 8.0.0a2), the HiDPI
+  `srcset` attribute and the `srcset()` method emit Thumbor URLs, and
+  `get_or_generate` heals legacy uid URLs (cached HTML, stale
+  `image_scales` catalog metadata) by parsing the deterministic
+  `{fieldname}-{width}-{md5}` uid and regenerating the info on the fly —
+  restricted to widths registered in `plone.allowed_sizes`. Review
+  hardening on top: srcset() mirrors the parent's edge-case guards
+  (zero-size original, original-size back-fill, unresolvable src scale),
+  and the HiDPI srcset path threads crop info through for scale infos
+  that carry a scale name.
+  Closes [#17](https://github.com/bluedynamics/plone-pgthumbor/issues/17).
+
 - Add `cdk8s-plone` to the ecosystem navigation dropdown in the docs.
 
+- Chore: apply ruff 0.16 markdown code-fence formatting to four docs files
+  (pre-existing drift; the QA workflow runs the latest ruff via uvx over
+  the whole repo). Mark up `zope2.Public` as inline code in a security-doc
+  heading so vale's Microsoft.Spacing rule no longer trips on it.
+
 ## 0.6.4 (2026-04-20)
 
 - Fix: `_needs_auth_url()` no longer issues a PostgreSQL query per image.
diff --git a/docs/sources/explanation/security.md b/docs/sources/explanation/security.md
index 691a36e..d8e35be 100644
--- a/docs/sources/explanation/security.md
+++ b/docs/sources/explanation/security.md
@@ -140,7 +140,7 @@ method:
 The auth handler is registered via Thumbor's `HANDLER_LISTS` configuration:
 
 ```python
-HANDLER_LISTS = ['zodb_pgjsonb_thumborblobloader.auth_handler']
+HANDLER_LISTS = ["zodb_pgjsonb_thumborblobloader.auth_handler"]
 ```
 
 `get_handlers()` returns a list of `(url_regex, handler_class, context)` tuples
@@ -206,7 +206,7 @@ Invalid or
    | Object not in catalog | 404 | Unknown object |
    | Database error | 503 | Service unavailable |
 
-### Why zope2.Public permission
+### Why `zope2.Public` permission
 
 The `@thumbor-auth` service is registered with `permission="zope2.Public"` -- it
 is accessible without authentication.
diff --git a/docs/sources/how-to/configure-thumbor.md b/docs/sources/how-to/configure-thumbor.md
index e20493b..d391fa9 100644
--- a/docs/sources/how-to/configure-thumbor.md
+++ b/docs/sources/how-to/configure-thumbor.md
@@ -52,7 +52,6 @@ HANDLER_LISTS = [
     "thumbor.handler_lists.healthcheck",
     "zodb_pgjsonb_thumborblobloader.auth_handler",
 ]
-
 ```
 
 The healthcheck handler must come first so `/healthcheck` is matched before
@@ -80,6 +79,7 @@ Can also be set via the `THUMBOR_SECURITY_KEY` environment variable:
 
 ```python
 import os
+
 SECURITY_KEY = os.environ.get("THUMBOR_SECURITY_KEY", "")
 ```
 
@@ -137,6 +137,7 @@ Both settings can be configured via environment variables:
 
 ```python
 import os
+
 AUTO_WEBP = os.environ.get("THUMBOR_AUTO_WEBP", "true").lower() in ("true", "1", "yes")
 AUTO_AVIF = os.environ.get("THUMBOR_AUTO_AVIF", "false").lower() in ("true", "1", "yes")
 ```
@@ -179,6 +180,7 @@ Can be configured via environment variable:
 
 ```python
 import os
+
 _detectors = os.environ.get("THUMBOR_DETECTORS", "")
 if _detectors:
     DETECTORS = [d.strip() for d in _detectors.split(",") if d.strip()]
@@ -227,6 +229,7 @@ Can be set via environment variable:
 
 ```python
 import os
+
 PGTHUMBOR_DSN = os.environ.get("PGTHUMBOR_DSN", "")
 ```
 
@@ -271,6 +274,7 @@ Can be set via environment variable:
 
 ```python
 import os
+
 PGTHUMBOR_PLONE_AUTH_URL = os.environ.get("PGTHUMBOR_PLONE_AUTH_URL", "")
 ```
 
diff --git a/docs/sources/how-to/write-crop-provider.md b/docs/sources/how-to/write-crop-provider.md
index 3c9158b..b59fa8a 100644
--- a/docs/sources/how-to/write-crop-provider.md
+++ b/docs/sources/how-to/write-crop-provider.md
@@ -21,7 +21,6 @@ from zope.interface import implementer
 
 @implementer(ICropProvider)
 class MyCropProvider:
-
     def __init__(self, context):
         self.context = context
 
diff --git a/docs/superpowers/plans/2026-04-13-hosting-aware-thumbor-urls.md b/docs/superpowers/plans/2026-04-13-hosting-aware-thumbor-urls.md
index 392d51e..e576159 100644
--- a/docs/superpowers/plans/2026-04-13-hosting-aware-thumbor-urls.md
+++ b/docs/superpowers/plans/2026-04-13-hosting-aware-thumbor-urls.md
@@ -108,9 +108,7 @@ class TestRootRelativeForm:
 
     def test_nested_path(self):
         assert (
-            resolve_thumbor_prefix(
-                "/img/thumbor", "https://site-a.example/subsite"
-            )
+            resolve_thumbor_prefix("/img/thumbor", "https://site-a.example/subsite")
             == "https://site-a.example/img/thumbor"
         )
 
@@ -180,9 +178,9 @@ class TestOutputShape:
         ["https://cdn.example/thumbor", "/thumbor", "thumbor"],
     )
     def test_no_trailing_slash(self, server_url):
-        assert not resolve_thumbor_prefix(
-            server_url, "https://plone.example"
-        ).endswith("/")
+        assert not resolve_thumbor_prefix(server_url, "https://plone.example").endswith(
+            "/"
+        )
 
     @pytest.mark.parametrize(
         "server_url,expected_prefix",
@@ -253,9 +251,7 @@ def resolve_thumbor_prefix(server_url: str, nav_root_url: str) -> str:
             has a query / fragment, or is otherwise malformed.
     """
     if not server_url or server_url.strip() != server_url:
-        raise ValueError(
-            "PGTHUMBOR_SERVER_URL is empty or has surrounding whitespace"
-        )
+        raise ValueError("PGTHUMBOR_SERVER_URL is empty or has surrounding whitespace")
     if "?" in server_url or "#" in server_url:
         raise ValueError(
             "PGTHUMBOR_SERVER_URL must not contain a query string or fragment"
@@ -410,30 +406,26 @@ Expected: the three `*_rejected` tests FAIL (no `ValueError` raised), the accept
 Modify [`src/plone/pgthumbor/config.py`](../../../src/plone/pgthumbor/config.py) — replace `__post_init__` with:
 
 ```python
-    def __post_init__(self):
-        from plone.pgthumbor.prefix import _ALLOWED_SCHEMES
+def __post_init__(self):
+    from plone.pgthumbor.prefix import _ALLOWED_SCHEMES
 
-        server_url = self.server_url
-        if not server_url or server_url.strip() != server_url:
-            raise ValueError(
-                "PGTHUMBOR_SERVER_URL is empty or has surrounding whitespace"
-            )
-        if "?" in server_url or "#" in server_url:
+    server_url = self.server_url
+    if not server_url or server_url.strip() != server_url:
+        raise ValueError("PGTHUMBOR_SERVER_URL is empty or has surrounding whitespace")
+    if "?" in server_url or "#" in server_url:
+        raise ValueError(
+            "PGTHUMBOR_SERVER_URL must not contain a query string or fragment"
+        )
+    if server_url.startswith(_ALLOWED_SCHEMES):
+        from urllib.parse import urlsplit
+
+        parts = urlsplit(server_url)
+        if not parts.netloc:
             raise ValueError(
-                "PGTHUMBOR_SERVER_URL must not contain a query string or "
-                "fragment"
+                f"PGTHUMBOR_SERVER_URL {server_url!r} has a scheme but no host"
             )
-        if server_url.startswith(_ALLOWED_SCHEMES):
-            from urllib.parse import urlsplit
-
-            parts = urlsplit(server_url)
-            if not parts.netloc:
-                raise ValueError(
-                    f"PGTHUMBOR_SERVER_URL {server_url!r} has a scheme "
-                    "but no host"
-                )
-        # Normalise: strip trailing slash
-        object.__setattr__(self, "server_url", server_url.rstrip("/"))
+    # Normalise: strip trailing slash
+    object.__setattr__(self, "server_url", server_url.rstrip("/"))
 ```
 
 - [ ] **Step 5: Run tests — all pass now**
@@ -696,17 +688,16 @@ import pytest
 @pytest.mark.parametrize(
     "server_url, nav_root, expected_prefix",
     [
-        ("https://cdn.example/thumbor", "https://site-a.example/2019",
-         "https://cdn.example/thumbor"),
-        ("/thumbor", "https://site-a.example/2019",
-         "https://site-a.example/thumbor"),
-        ("thumbor", "https://arch.example/2019",
-         "https://arch.example/2019/thumbor"),
+        (
+            "https://cdn.example/thumbor",
+            "https://site-a.example/2019",
+            "https://cdn.example/thumbor",
+        ),
+        ("/thumbor", "https://site-a.example/2019", "https://site-a.example/thumbor"),
+        ("thumbor", "https://arch.example/2019", "https://arch.example/2019/thumbor"),
     ],
 )
-def test_url_uses_configured_prefix(
-    monkeypatch, server_url, nav_root, expected_prefix
-):
+def test_url_uses_configured_prefix(monkeypatch, server_url, nav_root, expected_prefix):
     from plone.pgthumbor import scaling as scaling_mod
     from plone.pgthumbor.scaling import ThumborImageScale
 
@@ -717,9 +708,7 @@ def test_url_uses_configured_prefix(
     )
     nav_root_mock = MagicMock()
     nav_root_mock.absolute_url.return_value = nav_root
-    monkeypatch.setattr(
-        scaling_mod, "get_navigation_root", lambda c: nav_root_mock
-    )
+    monkeypatch.setattr(scaling_mod, "get_navigation_root", lambda c: nav_root_mock)
 
     ctx = MagicMock()
     ctx.absolute_url.return_value = f"{nav_root}/doc"
@@ -794,9 +783,7 @@ def _make_adapter(monkeypatch, server_url, nav_root):
     )
     nav_root_mock = MagicMock()
     nav_root_mock.absolute_url.return_value = nav_root
-    monkeypatch.setattr(
-        fa_mod, "get_navigation_root", lambda c: nav_root_mock
-    )
+    monkeypatch.setattr(fa_mod, "get_navigation_root", lambda c: nav_root_mock)
 
     field = MagicMock()
     field.__name__ = "image"
@@ -810,9 +797,7 @@ def _make_adapter(monkeypatch, server_url, nav_root):
 class TestScaleViewFromUrl:
     """The download value stored in image_scales metadata."""
 
-    def test_absolute_thumbor_url_stored_as_signed_path_marker(
-        self, monkeypatch
-    ):
+    def test_absolute_thumbor_url_stored_as_signed_path_marker(self, monkeypatch):
         adapter = _make_adapter(
             monkeypatch, "https://cdn.example/thumbor", "https://plone.example"
         )
@@ -821,12 +806,8 @@ class TestScaleViewFromUrl:
         )
         assert stored == "thumbor:/abc/300x200/fit-in/42/ff"
 
-    def test_root_relative_thumbor_url_stored_as_signed_path_marker(
-        self, monkeypatch
-    ):
-        adapter = _make_adapter(
-            monkeypatch, "/thumbor", "https://plone.example"
-        )
+    def test_root_relative_thumbor_url_stored_as_signed_path_marker(self, monkeypatch):
+        adapter = _make_adapter(monkeypatch, "/thumbor", "https://plone.example")
         stored = adapter._scale_view_from_url(
             "https://plone.example/thumbor/abc/300x200/fit-in/42/ff"
         )
@@ -835,9 +816,7 @@ class TestScaleViewFromUrl:
     def test_nav_root_relative_thumbor_url_stored_as_signed_path_marker(
         self, monkeypatch
     ):
-        adapter = _make_adapter(
-            monkeypatch, "thumbor", "https://arch.example/2019"
-        )
+        adapter = _make_adapter(monkeypatch, "thumbor", "https://arch.example/2019")
         stored = adapter._scale_view_from_url(
             "https://arch.example/2019/thumbor/abc/300x200/fit-in/42/ff"
         )
@@ -921,11 +900,9 @@ class ThumborImageScalesFieldAdapter(ImageFieldScales):
         cfg = get_thumbor_config()
         if cfg is not None:
             nav_root = get_navigation_root(self.context)
-            prefix = resolve_thumbor_prefix(
-                cfg.server_url, nav_root.absolute_url()
-            )
+            prefix = resolve_thumbor_prefix(cfg.server_url, nav_root.absolute_url())
             if url.startswith(prefix + "/") or url == prefix:
-                signed_path = url[len(prefix):] or "/"
+                signed_path = url[len(prefix) :] or "/"
                 return f"{THUMBOR_MARKER}{signed_path}"
         return super()._scale_view_from_url(url)
 ```
@@ -973,11 +950,17 @@ KEY = "test-secret-key"
 def _make_brain(download, field="image", width=300, height=200):
     brain = MagicMock()
     brain.image_scales = {
-        field: [{"scales": {"preview": {
-            "download": download,
-            "width": width,
-            "height": height,
-        }}}]
+        field: [
+            {
+                "scales": {
+                    "preview": {
+                        "download": download,
+                        "width": width,
+                        "height": height,
+                    }
+                }
+            }
+        ]
     }
     brain.getURL.return_value = "https://plone.example/folder/doc"
     brain.Title = "An Image"
@@ -1014,12 +997,21 @@ class TestThumborMarkerRendering:
     @pytest.mark.parametrize(
         "server_url, nav_root, expected_prefix",
         [
-            ("https://cdn.example/thumbor", "https://plone.example",
-             "https://cdn.example/thumbor"),
-            ("/thumbor", "https://site-a.example/2019",
-             "https://site-a.example/thumbor"),
-            ("thumbor", "https://arch.example/2019",
-             "https://arch.example/2019/thumbor"),
+            (
+                "https://cdn.example/thumbor",
+                "https://plone.example",
+                "https://cdn.example/thumbor",
+            ),
+            (
+                "/thumbor",
+                "https://site-a.example/2019",
+                "https://site-a.example/thumbor",
+            ),
+            (
+                "thumbor",
+                "https://arch.example/2019",
+                "https://arch.example/2019/thumbor",
+            ),
         ],
     )
     def test_marker_gets_resolved_with_current_prefix(
@@ -1028,9 +1020,7 @@ class TestThumborMarkerRendering:
         view = _make_view(monkeypatch, nav_root, server_url)
         brain = _make_brain("thumbor:/abc/300x200/fit-in/42/ff")
 
-        tag = view._tag_from_brain_image_scales(
-            brain, "image", scale="preview"
-        )
+        tag = view._tag_from_brain_image_scales(brain, "image", scale="preview")
 
         assert tag is not None
         assert f'src="{expected_prefix}/abc/300x200/fit-in/42/ff"' in tag
@@ -1044,26 +1034,17 @@ class TestLegacyDownloadRendering:
         )
         brain = _make_brain("https://legacy.example/foo/bar.jpg")
 
-        tag = view._tag_from_brain_image_scales(
-            brain, "image", scale="preview"
-        )
+        tag = view._tag_from_brain_image_scales(brain, "image", scale="preview")
         assert 'src="https://legacy.example/foo/bar.jpg"' in tag
 
-    def test_legacy_relative_download_concatenated_to_brain_url(
-        self, monkeypatch
-    ):
+    def test_legacy_relative_download_concatenated_to_brain_url(self, monkeypatch):
         view = _make_view(
             monkeypatch, "https://plone.example", "https://cdn.example/thumbor"
         )
         brain = _make_brain("@@images/uid-xyz.jpeg")
 
-        tag = view._tag_from_brain_image_scales(
-            brain, "image", scale="preview"
-        )
-        assert (
-            'src="https://plone.example/folder/doc/@@images/uid-xyz.jpeg"'
-            in tag
-        )
+        tag = view._tag_from_brain_image_scales(brain, "image", scale="preview")
+        assert 'src="https://plone.example/folder/doc/@@images/uid-xyz.jpeg"' in tag
 
 
 class TestMissingOrInvalidMetadata:
@@ -1074,8 +1055,7 @@ class TestMissingOrInvalidMetadata:
         brain = MagicMock()
         brain.image_scales = None
         assert (
-            view._tag_from_brain_image_scales(brain, "image", scale="preview")
-            is None
+            view._tag_from_brain_image_scales(brain, "image", scale="preview") is None
         )
 
     def test_thumbor_marker_without_config_falls_back(self, monkeypatch):
@@ -1085,8 +1065,7 @@ class TestMissingOrInvalidMetadata:
         view = _make_view(monkeypatch, "https://plone.example", server_url=None)
         brain = _make_brain("thumbor:/abc/300x200/42/ff")
         assert (
-            view._tag_from_brain_image_scales(brain, "image", scale="preview")
-            is None
+            view._tag_from_brain_image_scales(brain, "image", scale="preview") is None
         )
 ```
 
@@ -1107,9 +1086,7 @@ from plone.pgthumbor.field_adapter import THUMBOR_MARKER
 class ThumborNavigationRootScaling(NavigationRootScaling):
     """@@image_scale view that resolves Thumbor markers at render time."""
 
-    def _tag_from_brain_image_scales(
-        self, brain, fieldname, scale=None, **kwargs
-    ):
+    def _tag_from_brain_image_scales(self, brain, fieldname, scale=None, **kwargs):
         # Reuse the parent's validation / hidpi / lookup logic by
         # pulling the relevant stored dict ourselves — but we need to
         # handle our custom "thumbor:" marker before the parent's
@@ -1134,10 +1111,8 @@ class ThumborNavigationRootScaling(NavigationRootScaling):
                 # Thumbor not configured anymore; caller falls back
                 # to object-based rendering.
                 return None
-            signed_path = download[len(THUMBOR_MARKER):]
-            prefix = resolve_thumbor_prefix(
-                cfg.server_url, self.context.absolute_url()
-            )
+            signed_path = download[len(THUMBOR_MARKER) :]
+            prefix = resolve_thumbor_prefix(cfg.server_url, self.context.absolute_url())
             src = f"{prefix}{signed_path}"
             return self._render_image_tag(brain, data, src, **kwargs)
 
@@ -1146,8 +1121,9 @@ class ThumborNavigationRootScaling(NavigationRootScaling):
             brain, fieldname, scale=scale, **kwargs
         )
 
-    def _render_image_tag(self, brain, data, src, alt=_marker,
-                          css_class=None, title=_marker, **kwargs):
+    def _render_image_tag(
+        self, brain, data, src, alt=_marker, css_class=None, title=_marker, **kwargs
+    ):
         from plone.namedfile.scaling import _image_tag_from_values, _marker
 
         if title is _marker:
diff --git a/src/plone/pgthumbor/scaling.py b/src/plone/pgthumbor/scaling.py
index ca8632e..979ef2c 100644
--- a/src/plone/pgthumbor/scaling.py
+++ b/src/plone/pgthumbor/scaling.py
@@ -7,6 +7,8 @@
 from __future__ import annotations
 
 from AccessControl.PermissionRole import rolesForPermissionOn
+from plone.namedfile.scaling import _image_tag_from_values
+from plone.namedfile.scaling import _marker
 from plone.namedfile.scaling import ImageScale
 from plone.namedfile.scaling import ImageScaling
 from plone.pgthumbor.blob import get_blob_ids
@@ -14,6 +16,7 @@
 from plone.pgthumbor.interfaces import ICropProvider
 from plone.pgthumbor.url import scale_mode_to_thumbor
 from plone.pgthumbor.url import thumbor_url
+from plone.rfc822.interfaces import IPrimaryFieldInfo
 from ZODB.utils import u64
 from zope.component import queryAdapter
 
@@ -142,6 +145,27 @@ def _default_scale_url(context, uid, extension, base_url=None):
     return f"{base_url}/@@images/{uid}.{extension}"
 
 
+def _skip_type_fallback_url(context, data, fieldname, base_url=None):
+    """Original-field URL for types Thumbor cannot process (SVG).
+
+    Browsers scale vector images themselves; with the volatile
+    ThumborScaleStorage a uid-based scale URL can never resolve
+    (issue #17), so the field URL is the only stable target.  The
+    ``?v=`` modification-time cache buster compensates for the weaker
+    HTTP caching of non-unique URLs.
+    """
+    if base_url is None:
+        base_url = context.absolute_url()
+    url = f"{base_url}/@@images/{fieldname}"
+    modified = getattr(data, "modified", None)
+    if modified is None:
+        modified = getattr(context, "_p_mtime", None)
+    try:
+        return f"{url}?v={int(float(modified) * 1000)}"
+    except (TypeError, ValueError):
+        return url
+
+
 # True if installed plone.namedfile has _scale_url (>= 8.0.0a2)
 _HAS_SCALE_URL = hasattr(ImageScale, "_scale_url")
 
@@ -174,6 +198,10 @@ def __init__(self, context, request, **info):
             if url:
                 self._thumbor_url = url
                 self.url = url
+            elif getattr(self.data, "contentType", "") in _SKIP_THUMBOR_TYPES:
+                fieldname = info.get("fieldname") or getattr(self, "fieldname", None)
+                if fieldname:
+                    self.url = _skip_type_fallback_url(context, self.data, fieldname)
 
     def _scale_url(self, uid, extension, base_url=None, scale_info=None):
         """Generate Thumbor URL if possible, otherwise fall back to default."""
@@ -190,10 +218,45 @@ def _scale_url(self, uid, extension, base_url=None, scale_info=None):
             if url:
                 self._thumbor_url = url
                 return url
+        if scale_info and getattr(self.data, "contentType", "") in _SKIP_THUMBOR_TYPES:
+            fieldname = scale_info.get("fieldname") or getattr(self, "fieldname", None)
+            if fieldname:
+                return _skip_type_fallback_url(
+                    self.context, self.data, fieldname, base_url
+                )
         if _HAS_SCALE_URL:
             return super()._scale_url(uid, extension, base_url, scale_info=scale_info)
         return _default_scale_url(self.context, uid, extension, base_url)
 
+    def srcset_attribute(self):
+        """HiDPI srcset with Thumbor URLs — uid URLs never resolve here.
+
+        Skip-types get no srcset (vector scales itself); entries where no
+        Thumbor URL can be built are dropped rather than emitted dead.
+        """
+        if not self.srcset:
+            return ""
+        if getattr(self.data, "contentType", "") in _SKIP_THUMBOR_TYPES:
+            return ""
+        fieldname = getattr(self, "fieldname", None)
+        parts = []
+        for entry in self.srcset:
+            factor = entry.get("scale")
+            if not factor:
+                continue
+            crop = _get_crop(self.context, fieldname, entry)
+            url = _build_thumbor_url(
+                self.context,
+                self.data,
+                entry.get("width", 0) or 0,
+                entry.get("height", 0) or 0,
+                entry.get("mode", "scale"),
+                crop=crop,
+            )
+            if url:
+                parts.append(f"{url} {factor}x")
+        return ", ".join(parts)
+
     def index_html(self):
         """302 redirect to Thumbor URL instead of streaming ZODB data."""
         if self._thumbor_url:
@@ -223,6 +286,113 @@ def _scale_url(self, uid, extension, base_url=None, scale_info=None):
                 )
                 if url:
                     return url
+                if getattr(data, "contentType", "") in _SKIP_THUMBOR_TYPES:
+                    return _skip_type_fallback_url(
+                        self.context, data, scale_info["fieldname"], base_url
+                    )
         if _HAS_SCALE_URL:
             return super()._scale_url(uid, extension, base_url, scale_info=scale_info)
         return _default_scale_url(self.context, uid, extension, base_url)
+
+    def srcset(
+        self,
+        fieldname=None,
+        scale_in_src="huge",
+        sizes="",
+        alt=_marker,
+        css_class=None,
+        title=_marker,
+        **kwargs,
+    ):
+        """Reimplementation of plone.namedfile's srcset().
+
+        The parent builds ``@@images/{uid}`` URLs straight from
+        ``storage.pre_scale`` — dead under the volatile storage
+        (issue #17).  Build every URL from a scale view instead, whose
+        ``.url`` is a Thumbor URL (raster) or field URL (skip-types).
+        """
+        if fieldname is None:
+            try:
+                primary = IPrimaryFieldInfo(self.context, None)
+            except TypeError:
+                return
+            if primary is None:
+                return
+            fieldname = primary.fieldname
+
+        data = getattr(self.context, fieldname, None)
+        if getattr(data, "contentType", "") in _SKIP_THUMBOR_TYPES:
+            # Vector: one URL fits all widths — plain img tag suffices.
+            return self.tag(
+                fieldname=fieldname,
+                alt=alt,
+                css_class=css_class,
+                title=title,
+                **kwargs,
+            )
+
+        original_width, original_height = self.getImageSize(fieldname)
+        if not original_width or not original_height:
+            return None
+
+        srcset_urls = []
+
+        # Back-fill an original-size entry when no configured scale
+        # already covers it — mirrors the parent's guard so an
+        # undersized original still yields a non-empty srcset. The URL
+        # always comes from a scale view, never a bare uid string.
+        available_widths = [width for (width, _height) in self.available_sizes.values()]
+        if original_width not in available_widths:
+            scale_view = self.scale(
+                fieldname=fieldname,
+                width=original_width,
+                height=original_height,
+                pre=True,
+                include_srcset=False,
+            )
+            if scale_view is not None:
+                srcset_urls.append(f"{scale_view.url} {scale_view.width}w")
+
+        for _name, (width, height) in self.available_sizes.items():
+            if width <= original_width:
+                scale_view = self.scale(
+                    fieldname=fieldname,
+                    width=width,
+                    height=height,
+                    pre=True,
+                    include_srcset=False,
+                )
+                if scale_view is not None:
+                    srcset_urls.append(f"{scale_view.url} {scale_view.width}w")
+
+        attributes = {}
+        if title is _marker:
+            attributes["title"] = self.context.Title()
+        elif title:
+            attributes["title"] = title
+        if alt is _marker:
+            attributes["alt"] = self.context.Title()
+        else:
+            attributes["alt"] = alt
+        if css_class is not None:
+            attributes["class"] = css_class
+        attributes.update(**kwargs)
+        attributes["sizes"] = sizes
+        attributes["srcset"] = ", ".join(srcset_urls)
+
+        if scale_in_src not in self.available_sizes:
+            for key, (width, _height) in self.available_sizes.items():
+                if width <= original_width:
+                    scale_in_src = key
+                    break
+
+        scale_view = self.scale(fieldname=fieldname, scale=scale_in_src, pre=True)
+        if scale_view is None:
+            return None
+        attributes["src"] = scale_view.url
+        if "width" not in attributes:
+            attributes["width"] = scale_view.width
+        if "height" not in attributes:
+            attributes["height"] = scale_view.height
+
+        return _image_tag_from_values(*attributes.items())
diff --git a/src/plone/pgthumbor/storage.py b/src/plone/pgthumbor/storage.py
index 97b804d..939f79b 100644
--- a/src/plone/pgthumbor/storage.py
+++ b/src/plone/pgthumbor/storage.py
@@ -13,14 +13,38 @@
 from __future__ import annotations
 
 from plone.pgthumbor.interfaces import IPlonePgthumborLayer
+from plone.registry.interfaces import IRegistry
 from plone.scale.storage import AnnotationStorage
+from zope.component import queryUtility
 from zope.globalrequest import getRequest
 
 import logging
+import re
 
 
 logger = logging.getLogger(__name__)
 
+# plone.scale >= 4 deterministic uid: {fieldname}-{width}-{md5hex}
+_LEGACY_UID_RE = re.compile(
+    r"^(?P<fieldname>.+)-(?P<width>\d{1,9})-(?P<hash>[0-9a-f]{32})$"
+)
+
+
+def _allowed_scale_sizes():
+    """Map width -> (width, height) for all registered plone.allowed_sizes."""
+    registry = queryUtility(IRegistry)
+    if registry is None:
+        return {}
+    sizes = {}
+    for line in registry.get("plone.allowed_sizes") or ():
+        try:
+            _name, dims = line.split()
+            width, height = dims.split(":")
+            sizes.setdefault(int(width), (int(width), int(height)))
+        except ValueError:
+            continue
+    return sizes
+
 
 def thumbor_scale_storage_factory(context, modified=None):
     """Adapter factory that returns ThumborScaleStorage only when active.
@@ -67,12 +91,43 @@ def scale(self, **parameters):
         return self.pre_scale(**parameters)
 
     def get_or_generate(self, uid):
-        """Return stored info without generating image data.
+        """Return stored info, or heal a legacy uid without stored state.
 
-        Unlike the parent, never calls generate_scale() even if
-        data is None — in Thumbor mode, data is always None.
+        The volatile storage is empty on every fresh adapter instance, so
+        uid URLs from cached HTML or stale image_scales catalog metadata
+        would always 404 (issue #17).  The uid format is deterministic
+        and parseable — regenerate the info on the fly instead.
+        """
+        info = self.get(uid)
+        if info is not None:
+            return info
+        return self._heal_legacy_uid(uid)
+
+    def _heal_legacy_uid(self, uid):
+        """Rebuild scale info from a ``{fieldname}-{width}-{md5hex}`` uid.
+
+        Only widths registered in ``plone.allowed_sizes`` are accepted
+        (width 0 = original dimensions), so this cannot be abused to get
+        arbitrary dimensions signed on demand.  ``pre_scale`` itself
+        returns None for unknown fields or empty values.
         """
-        return self.get(uid)
+        match = _LEGACY_UID_RE.match(uid)
+        if match is None:
+            return None
+        fieldname = match.group("fieldname")
+        width = int(match.group("width"))
+        if width == 0:
+            dims = (None, None)
+        else:
+            dims = _allowed_scale_sizes().get(width)
+            if dims is None:
+                return None
+        info = self.pre_scale(
+            fieldname=fieldname, width=dims[0], height=dims[1], mode="scale"
+        )
+        if info is not None:
+            info.setdefault("fieldname", fieldname)
+        return info
 
     def generate_scale(self, uid=None, **parameters):
         """Override to prevent Pillow invocation.
diff --git a/tests/test_scaling.py b/tests/test_scaling.py
index ff840d9..25d6533 100644
--- a/tests/test_scaling.py
+++ b/tests/test_scaling.py
@@ -114,7 +114,8 @@ def test_tag_has_thumbor_src(self, monkeypatch):
         assert f'src="{scale.url}"' in tag
 
     def test_svg_fallback(self, monkeypatch):
-        """SVG images should use standard Plone URLs, not Thumbor."""
+        """SVG images must use the original field URL — uid URLs never
+        resolve under the volatile ThumborScaleStorage (issue #17)."""
         from plone.pgthumbor.scaling import ThumborImageScale
 
         _setup_env(monkeypatch)
@@ -122,6 +123,8 @@ def test_svg_fallback(self, monkeypatch):
         ctx.absolute_url.return_value = "http://plone:8080/doc"
         request = MagicMock()
         data = _mock_image_data(content_type="image/svg+xml")
+        data.modified = None
+        ctx._p_mtime = None
 
         scale = ThumborImageScale(
             ctx,
@@ -134,9 +137,94 @@ def test_svg_fallback(self, monkeypatch):
             mimetype="image/svg+xml",
         )
 
-        # SVG should use standard Plone URL
         assert SERVER not in scale.url
-        assert "@@images" in scale.url
+        assert scale.url == "http://plone:8080/doc/@@images/image"
+        assert "abc123" not in scale.url
+
+    def test_svg_fallback_cache_buster_from_field_modified(self, monkeypatch):
+        """When the field carries a modification time, append ?v=<millis>."""
+        from plone.pgthumbor.scaling import ThumborImageScale
+
+        _setup_env(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        data = _mock_image_data(content_type="image/svg+xml")
+        data.modified = 1700000000.0
+
+        scale = ThumborImageScale(
+            ctx,
+            MagicMock(),
+            data=data,
+            fieldname="image",
+            width=400,
+            height=300,
+            uid="image-400-abc123",
+            mimetype="image/svg+xml",
+        )
+
+        assert scale.url == "http://plone:8080/doc/@@images/image?v=1700000000000"
+
+    def test_svg_fallback_cache_buster_from_p_mtime(self, monkeypatch):
+        """Without field.modified, fall back to context._p_mtime."""
+        from plone.pgthumbor.scaling import ThumborImageScale
+
+        _setup_env(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        ctx._p_mtime = 1600000000.0
+        data = _mock_image_data(content_type="image/svg+xml")
+        data.modified = None
+
+        scale = ThumborImageScale(
+            ctx,
+            MagicMock(),
+            data=data,
+            fieldname="image",
+            width=400,
+            height=300,
+            uid="image-400-abc123",
+            mimetype="image/svg+xml",
+        )
+
+        assert scale.url == "http://plone:8080/doc/@@images/image?v=1600000000000"
+
+    def test_svg_fallback_legacy_namedfile_path(self, monkeypatch):
+        """The legacy (<8.0.0a2) __init__ branch must also emit the field
+        URL — production runs plone.namedfile 7.x."""
+        from plone.pgthumbor.scaling import ThumborImageScale
+
+        import plone.pgthumbor.scaling as scaling_mod
+
+        _setup_env(monkeypatch)
+        monkeypatch.setattr(scaling_mod, "_HAS_SCALE_URL", False)
+
+        from plone.pgthumbor.scaling import _default_scale_url
+
+        monkeypatch.setattr(
+            ThumborImageScale,
+            "_scale_url",
+            lambda self, uid, ext, base_url=None, scale_info=None: _default_scale_url(
+                self.context, uid, ext, base_url
+            ),
+        )
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        ctx._p_mtime = None
+        data = _mock_image_data(content_type="image/svg+xml")
+        data.modified = None
+
+        scale = ThumborImageScale(
+            ctx,
+            MagicMock(),
+            data=data,
+            fieldname="image",
+            width=400,
+            height=300,
+            uid="image-400-abc123",
+            mimetype="image/svg+xml",
+        )
+
+        assert scale.url == "http://plone:8080/doc/@@images/image"
 
     def test_not_configured_falls_back(self, monkeypatch):
         """When Thumbor not configured, use standard Plone URL."""
@@ -184,6 +272,109 @@ def test_original_image_no_thumbor(self, monkeypatch):
         assert "@@images" in scale.url
         assert SERVER not in scale.url
 
+    def test_srcset_attribute_uses_thumbor_urls(self, monkeypatch):
+        """HiDPI srcset entries must be Thumbor URLs, not dead uid URLs."""
+        from plone.pgthumbor.scaling import ThumborImageScale
+
+        _setup_env(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        data = _mock_image_data()
+
+        scale = ThumborImageScale(
+            ctx,
+            MagicMock(),
+            data=data,
+            fieldname="image",
+            width=400,
+            height=300,
+            uid="image-400-abc123",
+            mimetype="image/jpeg",
+            srcset=[
+                {"uid": "image-800-def456", "width": 800, "height": 600, "scale": 2},
+            ],
+        )
+
+        attr = scale.srcset_attribute()
+        assert attr.endswith(" 2x")
+        assert attr.startswith(SERVER)
+        assert "def456" not in attr
+
+    def test_srcset_attribute_empty_for_svg(self, monkeypatch):
+        """Vector images need no srcset — one URL fits all densities."""
+        from plone.pgthumbor.scaling import ThumborImageScale
+
+        _setup_env(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        ctx._p_mtime = None
+        data = _mock_image_data(content_type="image/svg+xml")
+        data.modified = None
+
+        scale = ThumborImageScale(
+            ctx,
+            MagicMock(),
+            data=data,
+            fieldname="image",
+            width=400,
+            height=300,
+            uid="image-400-abc123",
+            mimetype="image/svg+xml",
+            srcset=[
+                {"uid": "image-800-def456", "width": 800, "height": 600, "scale": 2},
+            ],
+        )
+
+        assert scale.srcset_attribute() == ""
+
+    def test_srcset_attribute_drops_unresolvable_entries(self, monkeypatch):
+        """No Thumbor config → entries are dropped, never emitted as uid URLs."""
+        from plone.pgthumbor.scaling import ThumborImageScale
+
+        env_override(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        data = _mock_image_data()
+
+        scale = ThumborImageScale(
+            ctx,
+            MagicMock(),
+            data=data,
+            fieldname="image",
+            width=400,
+            height=300,
+            uid="image-400-abc123",
+            mimetype="image/jpeg",
+            srcset=[
+                {"uid": "image-800-def456", "width": 800, "height": 600, "scale": 2},
+            ],
+        )
+
+        assert scale.srcset_attribute() == ""
+
+    def test_srcset_attribute_skips_entry_without_scale_factor(self, monkeypatch):
+        """A srcset entry lacking the 'scale' factor is skipped, not a KeyError."""
+        from plone.pgthumbor.scaling import ThumborImageScale
+
+        _setup_env(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        data = _mock_image_data()
+
+        scale = ThumborImageScale(
+            ctx,
+            MagicMock(),
+            data=data,
+            fieldname="image",
+            width=400,
+            height=300,
+            uid="image-400-abc123",
+            mimetype="image/jpeg",
+            srcset=[{"uid": "image-800-def456", "width": 800, "height": 600}],
+        )
+
+        assert scale.srcset_attribute() == ""
+
 
 class TestThumborImageScaling:
     """Test ThumborImageScaling (@@images view override)."""
@@ -636,6 +827,28 @@ def test_scale_url_fallback_no_fieldname(self, monkeypatch):
         result = scaling._scale_url("uid123", "jpeg")
         assert "@@images/uid123.jpeg" in result
 
+    def test_scale_url_svg_returns_field_url(self, monkeypatch):
+        """ThumborImageScaling._scale_url must not emit uid URLs for SVG."""
+        from plone.pgthumbor.scaling import ThumborImageScaling
+
+        _setup_env(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        ctx._p_mtime = None
+        svg = _mock_image_data(content_type="image/svg+xml")
+        svg.modified = None
+        ctx.logo = svg
+        view = ThumborImageScaling(ctx, MagicMock())
+
+        uid = "logo-200-" + "a" * 32
+        url = view._scale_url(
+            uid,
+            "svg",
+            scale_info={"fieldname": "logo", "width": 200, "height": 200, "uid": uid},
+        )
+
+        assert url == "http://plone:8080/doc/@@images/logo"
+
 
 class TestGetCrop:
     """Test _get_crop() helper."""
@@ -824,3 +1037,106 @@ def test_scaling_scale_url_with_crop(self, monkeypatch):
         )
         assert result.startswith(SERVER)
         assert "10x20:300x400" in result
+
+
+class TestThumborImageScalingSrcset:
+    """srcset() must never emit uid URLs (issue #17)."""
+
+    def _make_view(self, monkeypatch, content_type="image/jpeg"):
+        from plone.namedfile.scaling import ImageScaling
+        from plone.pgthumbor.scaling import ThumborImageScaling
+
+        _setup_env(monkeypatch)
+        ctx = MagicMock()
+        ctx.absolute_url.return_value = "http://plone:8080/doc"
+        ctx.Title.return_value = "Doc"
+        ctx.image = _mock_image_data(content_type=content_type)
+        view = ThumborImageScaling(ctx, MagicMock())
+        monkeypatch.setattr(
+            ImageScaling,
+            "available_sizes",
+            {"preview": (400, 400), "large": (800, 800)},
+            raising=False,
+        )
+        view.getImageSize = lambda fieldname: (800, 600)
+        return view
+
+    def test_srcset_uses_scale_view_urls(self, monkeypatch):
+        """Each configured size must be requested — and rendered — via its
+        own scale view, not a single mocked return_value that would mask
+        per-size behavior."""
+        view = self._make_view(monkeypatch)
+        calls = []
+
+        def fake_scale(fieldname=None, width=None, height=None, scale=None, **kw):
+            calls.append(
+                {
+                    "fieldname": fieldname,
+                    "width": width,
+                    "height": height,
+                    "scale": scale,
+                }
+            )
+            fake = MagicMock()
+            resolved_width = width or {"preview": 400, "large": 800}.get(scale, 400)
+            fake.url = f"{SERVER}/signed/{resolved_width}x0/42/ff"
+            fake.width = resolved_width
+            fake.height = resolved_width * 3 // 4
+            return fake
+
+        view.scale = MagicMock(side_effect=fake_scale)
+
+        tag = view.srcset(fieldname="image", scale_in_src="preview")
+
+        assert SERVER in tag
+        assert "@@images/image-" not in tag
+        assert "400w" in tag
+        assert "800w" in tag
+        requested_widths = {c["width"] for c in calls if c["width"] is not None}
+        assert requested_widths == {400, 800}
+        assert any(c["scale"] == "preview" for c in calls)
+
+    def test_srcset_svg_delegates_to_tag(self, monkeypatch):
+        from plone.namedfile.scaling import _marker
+
+        view = self._make_view(monkeypatch, content_type="image/svg+xml")
+        view.tag = MagicMock(return_value="<img/>")
+
+        result = view.srcset(fieldname="image")
+
+        assert result == "<img/>"
+        view.tag.assert_called_once_with(
+            fieldname="image", alt=_marker, css_class=None, title=_marker
+        )
+
+    def test_srcset_unresolvable_src_scale_returns_none(self, monkeypatch):
+        """An unresolvable scale_in_src must not raise AttributeError on
+        ``None.url`` — mirrors the parent's ``if scale is None: return
+        None`` guard (issue #17 fix round 1, Finding 1)."""
+        view = self._make_view(monkeypatch)
+        view.scale = MagicMock(return_value=None)
+
+        assert view.srcset(fieldname="image", scale_in_src="nonexistent") is None
+
+    def test_srcset_undersized_original_backfills_original_entry(self, monkeypatch):
+        """An original smaller than every configured scale must still get a
+        non-empty srcset, back-filled with an original-size scale-view URL
+        (issue #17 fix round 1, Finding 2)."""
+        view = self._make_view(monkeypatch)
+        view.getImageSize = lambda fieldname: (100, 80)
+        calls = []
+
+        def fake_scale(fieldname=None, scale=None, height=None, width=None, **kw):
+            calls.append({"scale": scale, "width": width, "height": height})
+            fake = MagicMock()
+            fake.url = f"{SERVER}/signed/{width or scale}/42/ff"
+            fake.width = width or 100
+            fake.height = height or 80
+            return fake
+
+        view.scale = MagicMock(side_effect=fake_scale)
+
+        tag = view.srcset(fieldname="image", scale_in_src="preview")
+
+        assert "srcset=" in tag
+        assert f"{SERVER}/signed/100/42/ff 100w" in tag
diff --git a/tests/test_storage.py b/tests/test_storage.py
index 955a8d9..b28f056 100644
--- a/tests/test_storage.py
+++ b/tests/test_storage.py
@@ -101,6 +101,164 @@ def test_separate_instances_separate_storage(self):
         s1.storage["key"] = "value"
         assert "key" not in s2.storage
 
+    def test_get_or_generate_heals_legacy_uid(self):
+        """A uid-shaped miss regenerates scale info via pre_scale (issue #17):
+        cached HTML and stale image_scales metadata keep working."""
+        storage = _make_storage()
+        healed = {
+            "uid": "image-400-" + "a" * 32,
+            "data": None,
+            "width": 400,
+            "height": 400,
+        }
+
+        with (
+            patch.object(storage, "pre_scale", return_value=dict(healed)) as mock_pre,
+            patch(
+                "plone.pgthumbor.storage._allowed_scale_sizes",
+                return_value={400: (400, 400)},
+            ),
+        ):
+            result = storage.get_or_generate("image-400-" + "b" * 32)
+
+        mock_pre.assert_called_once_with(
+            fieldname="image", width=400, height=400, mode="scale"
+        )
+        assert result["fieldname"] == "image"
+
+    def test_get_or_generate_heals_fieldname_with_dashes(self):
+        """fieldname may contain dashes — parse from the right."""
+        storage = _make_storage()
+
+        with (
+            patch.object(storage, "pre_scale", return_value={"uid": "x"}) as mock_pre,
+            patch(
+                "plone.pgthumbor.storage._allowed_scale_sizes",
+                return_value={200: (200, 200)},
+            ),
+        ):
+            storage.get_or_generate("my-logo-field-200-" + "c" * 32)
+
+        mock_pre.assert_called_once_with(
+            fieldname="my-logo-field", width=200, height=200, mode="scale"
+        )
+
+    def test_get_or_generate_rejects_unregistered_width(self):
+        """Unknown widths 404 — prevents on-demand signing of arbitrary
+        dimensions (cache-filling amplification)."""
+        storage = _make_storage()
+
+        with (
+            patch.object(storage, "pre_scale") as mock_pre,
+            patch(
+                "plone.pgthumbor.storage._allowed_scale_sizes",
+                return_value={400: (400, 400)},
+            ),
+        ):
+            assert storage.get_or_generate("image-999-" + "b" * 32) is None
+
+        mock_pre.assert_not_called()
+
+    def test_get_or_generate_rejects_malformed_uid(self):
+        """Hash part must look like md5-hex; anything else stays a 404."""
+        storage = _make_storage()
+
+        with patch.object(storage, "pre_scale") as mock_pre:
+            assert storage.get_or_generate("image-400-nothex") is None
+            assert storage.get_or_generate("image-400") is None
+
+        mock_pre.assert_not_called()
+
+    def test_get_or_generate_width_zero_means_original(self):
+        """uid 'image-0-<hash>' comes from bare tag()/pre_scale without a
+        width — regenerate with original dimensions."""
+        storage = _make_storage()
+
+        with (
+            patch.object(storage, "pre_scale", return_value={"uid": "x"}) as mock_pre,
+            patch(
+                "plone.pgthumbor.storage._allowed_scale_sizes",
+                return_value={},
+            ),
+        ):
+            storage.get_or_generate("image-0-" + "d" * 32)
+
+        mock_pre.assert_called_once_with(
+            fieldname="image", width=None, height=None, mode="scale"
+        )
+
+    def test_get_or_generate_pre_scale_none_returns_none(self):
+        """pre_scale returning None (missing field/value) stays a 404."""
+        storage = _make_storage()
+
+        with (
+            patch.object(storage, "pre_scale", return_value=None),
+            patch(
+                "plone.pgthumbor.storage._allowed_scale_sizes",
+                return_value={400: (400, 400)},
+            ),
+        ):
+            assert storage.get_or_generate("gone-400-" + "e" * 32) is None
+
+    def test_get_or_generate_rejects_oversized_width(self):
+        """A multi-thousand-digit width must not raise — reject with None."""
+        storage = _make_storage()
+
+        with patch.object(storage, "pre_scale") as mock_pre:
+            assert (
+                storage.get_or_generate("image-" + "9" * 5000 + "-" + "a" * 32) is None
+            )
+
+        mock_pre.assert_not_called()
+
+
+class TestAllowedScaleSizes:
+    """Direct tests for the registry-parsing DoS gate."""
+
+    def _registry_with(self, lines):
+        registry = MagicMock()
+        registry.get.return_value = lines
+        return registry
+
+    def test_parses_registered_sizes(self):
+        from plone.pgthumbor.storage import _allowed_scale_sizes
+
+        registry = self._registry_with(["preview 400:400", "large 800:65536"])
+        with patch("plone.pgthumbor.storage.queryUtility", return_value=registry):
+            sizes = _allowed_scale_sizes()
+
+        assert sizes == {400: (400, 400), 800: (800, 65536)}
+        registry.get.assert_called_once_with("plone.allowed_sizes")
+
+    def test_first_width_wins_on_duplicates(self):
+        from plone.pgthumbor.storage import _allowed_scale_sizes
+
+        registry = self._registry_with(["a 400:400", "b 400:300"])
+        with patch("plone.pgthumbor.storage.queryUtility", return_value=registry):
+            assert _allowed_scale_sizes() == {400: (400, 400)}
+
+    def test_skips_malformed_lines(self):
+        from plone.pgthumbor.storage import _allowed_scale_sizes
+
+        registry = self._registry_with(
+            ["broken", "no-dims 400", "preview 400:400", "bad 400x300"]
+        )
+        with patch("plone.pgthumbor.storage.queryUtility", return_value=registry):
+            assert _allowed_scale_sizes() == {400: (400, 400)}
+
+    def test_no_registry_returns_empty(self):
+        from plone.pgthumbor.storage import _allowed_scale_sizes
+
+        with patch("plone.pgthumbor.storage.queryUtility", return_value=None):
+            assert _allowed_scale_sizes() == {}
+
+    def test_none_record_returns_empty(self):
+        from plone.pgthumbor.storage import _allowed_scale_sizes
+
+        registry = self._registry_with(None)
+        with patch("plone.pgthumbor.storage.queryUtility", return_value=registry):
+            assert _allowed_scale_sizes() == {}
+
 
 class TestThumborScaleStorageFactory:
     """Test that the factory respects the browser layer."""