diff --git a/dbschema/default.esdl b/dbschema/default.esdl
index 26a3fe9..dcc7154 100644
--- a/dbschema/default.esdl
+++ b/dbschema/default.esdl
@@ -19,10 +19,12 @@ module default {
     }
     required single type: GameType {
       readonly := true;
+      constraint exclusive;
       on source delete delete target;
     }
     required single ruleset: Ruleset {
       readonly := true;
+      constraint exclusive;
       on source delete delete target;
     }
     required winner: str {