diff --git a/oauthenticator/openshift.py b/oauthenticator/openshift.py
index 534a67e3..b103558c 100644
--- a/oauthenticator/openshift.py
+++ b/oauthenticator/openshift.py
@@ -116,8 +116,10 @@ async def user_is_authorized(self, auth_model):
             # User is authorized if either in allowed_groups or in admin_groups
             all_allowed_groups = self.allowed_groups
             if self.admin_groups:
-                all_allowed_groups = all_allowed_groups.unions(self.admin_groups)
-            if not self.user_groups_in_allowed_groups(user_groups, all_allowed_groups):
+                all_allowed_groups = all_allowed_groups.union(self.admin_groups)
+            if not self.user_groups_in_allowed_groups(
+                user_groups, all_allowed_groups
+            ):
                 self.log.warning(msg)
                 return False