@@ -6206,6 +6206,8 @@ structmeta_collect_fields(StructMetaInfo *info, MsgspecState *mod, bool kwonly)
 
         if (structmeta_process_default(info, field) < 0) goto error;
     }
+    Py_DECREF(annotations);
+    Py_XDECREF(module_ns);
     return 0;
 error:
     Py_DECREF(annotations);
 
@@ -946,6 +946,69 @@ class Test(Struct):
     assert sys.getrefcount(data) <= 4
 
 
+def test_struct_definition_does_not_leak_annotations():
+    """Defining a struct type must not retain its `__annotations__` dict"""
+
+    class Annotation:
+        pass
+
+    ref = weakref.ref(Annotation)
+
+    cls = defstruct("Temp", [("x", Annotation)])
+    del cls, Annotation
+    gc.collect()
+
+    assert ref() is None
+
+
+def test_struct_definition_does_not_leak_class_body_annotations():
+    """A class body must not retain the annotations built for it"""
+
+    def define_struct_type():
+        class Annotation:
+            pass
+
+        class Example(Struct):
+            x: Annotation
+
+        return weakref.ref(Annotation)
+
+    refs = [define_struct_type() for _ in range(3)]
+    gc.collect()
+
+    assert [ref() for ref in refs] == [None, None, None]
+
+
+@pytest.mark.parametrize("spelling", ["ClassVar", "typing.ClassVar"])
+def test_struct_definition_does_not_leak_module_namespace(spelling):
+    """A string `ClassVar` annotation must not retain the module namespace"""
+
+    class Sentinel:
+        pass
+
+    def define_in_temp_module():
+        with temp_module(
+            "import typing\nfrom typing import ClassVar\nimport msgspec\n"
+        ) as mod:
+            sentinel = Sentinel()
+            mod.__dict__["sentinel"] = sentinel
+            exec(
+                "from __future__ import annotations\n"
+                "class Ex(msgspec.Struct):\n"
+                f"    a: {spelling}[int] = 1\n"
+                "    x: int = 0\n",
+                mod.__dict__,
+            )
+            # The leak only exists while the annotations are strings
+            assert mod.Ex.__annotations__["x"] == "int"
+            return weakref.ref(sentinel)
+
+    refs = [define_in_temp_module() for _ in range(3)]
+    gc.collect()
+
+    assert [ref() for ref in refs] == [None, None, None]
+
+
 def test_struct_gc_not_added_if_not_needed():
     """Structs aren't tracked by GC until/unless they reference a container type"""
Original file line number	Diff line number	Diff line change
`@@ -6206,6 +6206,8 @@ structmeta_collect_fields(StructMetaInfo info, MsgspecState mod, bool kwonly)`
`6206`	`6206`
`6207`	`6207`	`if (structmeta_process_default(info, field) < 0) goto error;`
`6208`	`6208`	`}`
	`6209`	`+ Py_DECREF(annotations);`
	`6210`	`+ Py_XDECREF(module_ns);`
`6209`	`6211`	`return 0;`
`6210`	`6212`	`error:`
`6211`	`6213`	`Py_DECREF(annotations);`