diff --git a/npm/ng-packs/packages/core/src/lib/utils/date-extensions.ts b/npm/ng-packs/packages/core/src/lib/utils/date-extensions.ts
index 3522b000c8..8f0d17504d 100644
--- a/npm/ng-packs/packages/core/src/lib/utils/date-extensions.ts
+++ b/npm/ng-packs/packages/core/src/lib/utils/date-extensions.ts
@@ -2,7 +2,7 @@ export {};
 
 declare global {
   interface Date {
-    toLocalISOString(): string;
+    toLocalISOString?: () => string;
   }
 }