diff --git a/python/keepass/kpdb.py b/python/keepass/kpdb.py
index fb7f6e5..eda6bed 100644
--- a/python/keepass/kpdb.py
+++ b/python/keepass/kpdb.py
@@ -261,7 +261,7 @@ def gen_groupid(self):
         """
         Generate a new groupid (4-byte value that isn't 0 or 0xffffffff).
         """
-        existing_groupids = {group.groupid for group in self.groups}
+        existing_groupids = set(group.groupid for group in self.groups)
         if len(existing_groupids) >= 0xfffffffe:
             raise Exception("All groupids are in use!")
         while True: