diff --git a/comtypes/typeinfo.py b/comtypes/typeinfo.py
index 4a3bf152..1df759fa 100644
--- a/comtypes/typeinfo.py
+++ b/comtypes/typeinfo.py
@@ -632,7 +632,11 @@ def LoadTypeLib(szFile: str) -> ITypeLib:
 
 
 def UnRegisterTypeLib(
-    libID: str, wVerMajor: int, wVerMinor: int, lcid: int = 0, syskind: int = SYS_WIN32
+    libID: str,
+    wVerMajor: int,
+    wVerMinor: int,
+    lcid: int = 0,
+    syskind: int = (SYS_WIN64 if is_64_bit else SYS_WIN32),
 ) -> int:
     """Unregister a registered type library"""
     return _oleaut32.UnRegisterTypeLib(