diff --git a/CHANGES.rst b/CHANGES.rst
index ad6d698341a..1e986521c80 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -13,6 +13,11 @@ Bugs fixed
   English stemmer) and Dutch (which uses the Dutch Porter stemmer).
   Patch by Hugo van Kemenade
 
+* #14221: Fix a regression from Sphinx v8.2.0 onwards that could cause links
+  produced by ``singlehtml`` builds to contain multiple fragment delimiters
+  (``#``), and withdraw the deprecation of
+  ``SingleFileHTMLBuilder.fix_refuris`` because the builder still requires it.
+  Patch by James Addison
 
 Release 9.1.0 (released Dec 31, 2025)
 =====================================
diff --git a/doc/extdev/deprecated.rst b/doc/extdev/deprecated.rst
index b7583b0e37d..79323233e6d 100644
--- a/doc/extdev/deprecated.rst
+++ b/doc/extdev/deprecated.rst
@@ -52,11 +52,6 @@ The following is a list of deprecated interfaces.
      - 11.0
      - N/A
 
-   * - ``sphinx.builders.singlehtml.SingleFileHTMLBuilder.fix_refuris``
-     - 8.2
-     - 10.0
-     - N/A
-
    * - ``sphinx.util.FilenameUniqDict``
      - 8.1
      - 10.0
diff --git a/sphinx/builders/singlehtml.py b/sphinx/builders/singlehtml.py
index 1888f6679d1..cd55261537d 100644
--- a/sphinx/builders/singlehtml.py
+++ b/sphinx/builders/singlehtml.py
@@ -2,14 +2,12 @@
 
 from __future__ import annotations
 
-import warnings
 from typing import TYPE_CHECKING
 
 from docutils import nodes
 
 from sphinx._cli.util.colour import darkgreen
 from sphinx.builders.html import StandaloneHTMLBuilder
-from sphinx.deprecation import RemovedInSphinx10Warning
 from sphinx.environment.adapters.toctree import global_toctree_for_doc
 from sphinx.locale import __
 from sphinx.util import logging
@@ -52,14 +50,6 @@ def get_relative_uri(self, from_: str, to: str, typ: str | None = None) -> str:
         return self.get_target_uri(to, typ)
 
     def fix_refuris(self, tree: Node) -> None:
-        deprecation_msg = (
-            "The 'SingleFileHTMLBuilder.fix_refuris' method is no longer used "
-            'within the builder and is planned for removal in Sphinx 10. '
-            'Please report malformed URIs generated by the Sphinx singlehtml '
-            'builder as bugreports.'
-        )
-        warnings.warn(deprecation_msg, RemovedInSphinx10Warning, stacklevel=2)
-
         # fix refuris with double anchor
         for refnode in tree.findall(nodes.reference):
             if 'refuri' not in refnode:
@@ -86,6 +76,8 @@ def _get_local_toctree(
         toctree = global_toctree_for_doc(
             self.env, docname, self, tags=self.tags, collapse=collapse, **kwargs
         )
+        if toctree is not None:
+            self.fix_refuris(toctree)
         return self.render_partial(toctree)['fragment']
 
     def assemble_doctree(self) -> nodes.document:
@@ -95,6 +87,7 @@ def assemble_doctree(self) -> nodes.document:
         tree = inline_all_toctrees(self, set(), master, tree, darkgreen, [master])
         tree['docname'] = master
         self.env.resolve_references(tree, master, self)
+        self.fix_refuris(tree)
         return tree
 
     def assemble_toc_secnumbers(self) -> dict[str, dict[str, tuple[int, ...]]]:
@@ -145,6 +138,7 @@ def get_doc_context(self, docname: str, body: str, metatags: str) -> dict[str, A
         )
         # if there is no toctree, toc is None
         if toctree:
+            self.fix_refuris(toctree)
             toc = self.render_partial(toctree)['fragment']
             display_toc = True
         else:
diff --git a/tests/roots/test-refuris/conf.py b/tests/roots/test-refuris/conf.py
new file mode 100644
index 00000000000..b490ae6b4da
--- /dev/null
+++ b/tests/roots/test-refuris/conf.py
@@ -0,0 +1,2 @@
+project = 'Glossary Test'
+extensions = []
diff --git a/tests/roots/test-refuris/glossary/term1.rst b/tests/roots/test-refuris/glossary/term1.rst
new file mode 100644
index 00000000000..4c7cbfdd0dc
--- /dev/null
+++ b/tests/roots/test-refuris/glossary/term1.rst
@@ -0,0 +1,7 @@
+Glossary
+========
+
+.. glossary::
+
+   API
+      Lorem Ipsum.
diff --git a/tests/roots/test-refuris/index.rst b/tests/roots/test-refuris/index.rst
new file mode 100644
index 00000000000..c044ca8a538
--- /dev/null
+++ b/tests/roots/test-refuris/index.rst
@@ -0,0 +1,12 @@
+Main Documentation
+==================
+
+This documentation discusses :term:`API` design.
+
+We use :term:`API` throughout our application to communicate between
+different services.
+
+.. toctree::
+   :maxdepth: 2
+
+   glossary/term1
diff --git a/tests/test_builders/test_build_html_refuris.py b/tests/test_builders/test_build_html_refuris.py
new file mode 100644
index 00000000000..99ebaf26a68
--- /dev/null
+++ b/tests/test_builders/test_build_html_refuris.py
@@ -0,0 +1,58 @@
+"""Test output of reference URIs when building single-page HTML output."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+import pytest
+
+from tests.test_builders.xpath_util import check_xpath
+
+if TYPE_CHECKING:
+    from collections.abc import Callable, Sequence
+    from pathlib import Path
+    from xml.etree.ElementTree import Element, ElementTree
+
+    from sphinx.testing.util import SphinxTestApp
+
+
+def _internal_reference_fragment_check(nodes: Sequence[Element]) -> None:
+    """Confirm that internal references do not contain duplicate fragment symbols"""
+    assert nodes, 'Expected at least one node to check'
+    for node in nodes:
+        assert node.tag == 'a', 'Attempted to check hyperlink on a non-anchor element'
+        href = node.attrib.get('href')
+        if not href:
+            continue
+        assert href.count('#') < 2, 'Hyperlink contains duplicate fragments'
+
+
+@pytest.mark.sphinx('singlehtml', testroot='refuris')
+def test_singlehtml_refuris_check_fragments(
+    app: SphinxTestApp,
+    cached_etree_parse: Callable[[Path], ElementTree],
+) -> None:
+    app.build()
+    check_xpath(
+        cached_etree_parse(app.outdir / 'index.html'),
+        'index.html',
+        ".//a[@class='reference internal']",
+        _internal_reference_fragment_check,
+    )
+
+
+@pytest.mark.sphinx('singlehtml', testroot='refuris')
+def test_singlehtml_refuris_check_term_anchor(
+    app: SphinxTestApp,
+    cached_etree_parse: Callable[[Path], ElementTree],
+) -> None:
+    app.build()
+    etree = cached_etree_parse(app.outdir / 'index.html')
+    api_refs = [
+        node
+        for node in etree.findall(".//a[@class='reference internal']")
+        if ''.join(node.itertext()) == 'API'
+    ]
+    assert api_refs  # the API term is referenced twice from the document text
+    assert all(ref.get('href') == '#term-API' for ref in api_refs)
+    assert etree.find(".//*[@id='term-API']") is not None