diff --git a/src/py/lib/test_twine.py b/src/py/lib/test_twine.py
index ae21076d..d4644683 100644
--- a/src/py/lib/test_twine.py
+++ b/src/py/lib/test_twine.py
@@ -9,6 +9,16 @@ def test_leb128():
     c = twine.Decoder(b'\x81\x42')
     assert c._leb128(off=0)[0] == ((0x42 << 7) + 1)  # pyright: ignore[reportPrivateUsage]
 
+def test_caches_are_per_instance():
+    # Regression: `Decoder.caches` must not be shared across instances, otherwise
+    # cached values keyed by offset leak from one artifact's decoder into another's,
+    # returning stale decoded sub-values at colliding offsets.
+    d1 = twine.Decoder(b'\x00')
+    d2 = twine.Decoder(b'\x00')
+    assert d1.caches is not d2.caches
+    d1.caches.setdefault('T', {})[42] = 'stale'
+    assert 42 not in d2.caches.get('T', {})
+
 def _get_testdata1() -> twine.Decoder:
     with open('test_data/typereg.twine', 'rb') as f:
         data = bytearray(f.read())
diff --git a/src/py/lib/twine.py b/src/py/lib/twine.py
index 25ea94b4..68d753b6 100644
--- a/src/py/lib/twine.py
+++ b/src/py/lib/twine.py
@@ -17,12 +17,13 @@ class Error(Exception):
 class Decoder:
     """A twine decoder"""
 
-    # per-type cache
-    caches: dict[str, dict[offset, Any]] = {}
+    # per-type cache, keyed by offset; must be per-instance (per-artifact),
+    caches: dict[str, dict[offset, Any]]
 
     def __init__(self, a: bytearray | bytes):
         a = bytearray(a)
         self.bs = a
+        self.caches = {}
 
     def __first_byte(self, off: int) -> tuple[int, int]:
         c = self.bs[off]
diff --git a/src/py/pyproject.toml b/src/py/pyproject.toml
index 7e0bb0fe..563bc4d6 100644
--- a/src/py/pyproject.toml
+++ b/src/py/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "imandrax_api"
-version = "0.20"
+version = "0.20.1"
 description = "Imandrax API client library"
 requires-python = ">=3.12"
 dependencies = [
diff --git a/src/py/setup.py b/src/py/setup.py
index 0d3f0cca..a05f6ae6 100644
--- a/src/py/setup.py
+++ b/src/py/setup.py
@@ -1,6 +1,6 @@
 from setuptools import setup
 
-VERSION = "0.20"
+VERSION = "0.20.1"
 setup(
     name="imandrax_api",
     version=VERSION,
diff --git a/src/py/uv.lock b/src/py/uv.lock
index 5928b302..73f63b44 100644
--- a/src/py/uv.lock
+++ b/src/py/uv.lock
@@ -284,7 +284,7 @@ wheels = [
 
 [[package]]
 name = "imandrax-api"
-version = "0.20"
+version = "0.20.1"
 source = { editable = "." }
 dependencies = [
     { name = "protobuf" },