diff --git a/mypy/stubtest.py b/mypy/stubtest.py
index 39b27a1f1ed3..f9e6f7d337be 100644
--- a/mypy/stubtest.py
+++ b/mypy/stubtest.py
@@ -1541,6 +1541,7 @@ def verify_typealias(
         "__getinitargs__",
         "__reduce_ex__",
         "__reduce__",
+        "__slotnames__",  # Cached names of slots added by `copyreg` module.
         # ctypes weirdness
         "__ctype_be__",
         "__ctype_le__",