diff --git a/packages/mobx/src/types/observableobject.ts b/packages/mobx/src/types/observableobject.ts
index b02c237a5..a24b4a8c6 100644
--- a/packages/mobx/src/types/observableobject.ts
+++ b/packages/mobx/src/types/observableobject.ts
@@ -629,7 +629,7 @@ export class ObservableObjectAdministration
         this.keysAtom_.reportChanged()
     }
 
-    ownKeys_(): ArrayLike<string | symbol> {
+    ownKeys_(): Array<string | symbol> {
         this.keysAtom_.reportObserved()
         return ownKeys(this.target_)
     }