diff --git a/src/patchy/api.py b/src/patchy/api.py
index d014aed..d87aca6 100644
--- a/src/patchy/api.py
+++ b/src/patchy/api.py
@@ -299,11 +299,18 @@ def _process_function() -> ast.Module:
 
     # Compile and retrieve the new Code object
     localz: dict[str, Any] = {}
+
+    globalz = func.__globals__.copy()
+    for cell in func.__closure__ or ():
+        cell_contents = cell.cell_contents
+        if isinstance(cell_contents, type):
+            globalz.update(cell_contents.__dict__)
+
     new_code = cast(CodeType, _compile(new_source))
 
     exec(
         new_code,
-        dict(func.__globals__),
+        globalz,
         localz,
     )
     new_func = localz["__patchy_freevars__"]()
diff --git a/tests/test_patch.py b/tests/test_patch.py
index 785b030..e5ddc11 100644
--- a/tests/test_patch.py
+++ b/tests/test_patch.py
@@ -795,6 +795,49 @@ def bark() -> str:
     assert Doge.bark() == "Wowowow"
 
 
+def test_patch_closure_use_function():
+    DEFAULT_MEDIUM = "Chalk"
+
+    def paint(medium: str = DEFAULT_MEDIUM) -> str:
+        return medium
+
+    assert paint() == "Chalk"
+
+    patchy.patch(
+        paint,
+        """\
+        @@ -1,2 +1,2 @@
+         def paint(medium: str = DEFAULT_MEDIUM) -> str:
+        -    return medium
+        +    return "Cheese"
+        """,
+    )
+
+    assert paint() == "Cheese"
+
+
+def test_patch_closure_use_instancemethod():
+    class Artist:
+        DEFAULT_MEDIUM = "Chalk"
+
+        def paint(self, medium: str = DEFAULT_MEDIUM) -> str:
+            return medium
+
+    assert Artist().paint() == "Chalk"
+
+    patchy.patch(
+        Artist.paint,
+        """\
+        @@ -1,2 +1,2 @@
+         def paint(self, medium: str = DEFAULT_MEDIUM) -> str:
+        -    return medium
+        +    return "Cheese"
+        """,
+    )
+
+    assert Artist().paint() == "Cheese"
+
+
 def test_patch_future_python(tmp_path):
     (tmp_path / "future_user.py").write_text(
         dedent(