diff --git a/tests/inputs/proto3_field_presence/test_proto3_field_presence.py b/tests/inputs/proto3_field_presence/test_proto3_field_presence.py
index 3972d86..e311199 100644
--- a/tests/inputs/proto3_field_presence/test_proto3_field_presence.py
+++ b/tests/inputs/proto3_field_presence/test_proto3_field_presence.py
@@ -41,3 +41,8 @@ def test_null_fields_json():
         "test8": None,
         "test9": None,
     }
+
+
+def test_unset_access():  # see #523
+    assert Test().test1 is None
+    assert Test(test1=None).test1 is None