diff --git a/src/system/game-data.ts b/src/system/game-data.ts
index a9726ac0713..4d01ae9998a 100644
--- a/src/system/game-data.ts
+++ b/src/system/game-data.ts
@@ -679,7 +679,7 @@ export class GameData {
         return ret;
       }
 
-      return k.endsWith("Attr") && ![ "natureAttr", "abilityAttr", "passiveAttr" ].includes(k) ? BigInt(v) : v;
+      return k.endsWith("Attr") && ![ "natureAttr", "abilityAttr", "passiveAttr" ].includes(k) ? BigInt(v ?? 0) : v;
     }) as SystemSaveData;
   }