diff --git a/python_multipart/multipart.py b/python_multipart/multipart.py
index 5237786..cfc3220 100644
--- a/python_multipart/multipart.py
+++ b/python_multipart/multipart.py
@@ -1759,9 +1759,9 @@ def on_part_data(data: bytes, start: int, end: int) -> None:
                 # TODO: check for error here.
 
             def on_part_end() -> None:
-                nonlocal f_multi, is_file
                 assert f_multi is not None
-                f_multi.finalize()
+                assert writer is not None
+                writer.finalize()
                 if is_file:
                     if on_file:
                         assert isinstance(f_multi, File)
@@ -1833,9 +1833,6 @@ def on_headers_finished() -> None:
                         writer = f_multi
 
             def _on_end() -> None:
-                nonlocal writer
-                if writer is not None:
-                    writer.finalize()
                 if self.on_end is not None:
                     self.on_end()
 
diff --git a/tests/test_multipart.py b/tests/test_multipart.py
index 9ad3fdc..de220eb 100644
--- a/tests/test_multipart.py
+++ b/tests/test_multipart.py
@@ -854,6 +854,20 @@ def test_content_transfer_encoding_is_case_insensitive(content_transfer_encoding
     assert file.file_object.read() == b"Test"
 
 
+def test_finalizes_transfer_encoding_before_callback() -> None:
+    data = (
+        b'--b\r\nContent-Disposition: form-data; name="f"\r\n'
+        b"Content-Transfer-Encoding: quoted-printable\r\n\r\n=4\r\n--b--\r\n"
+    )
+    values: list[bytes | None] = []
+    parser = FormParser("multipart/form-data", lambda field: values.append(field.value), None, boundary=b"b")
+
+    parser.write(data)
+    parser.finalize()
+
+    assert values == [b"=4"]
+
+
 def test_parser_states_remain_enum_members() -> None:
     multipart_parser = MultipartParser(b"boundary")
     multipart_parser.write(b"--boundary--\r\n")