diff --git a/packages/tswebextension/src/lib/mv2/background/app.ts b/packages/tswebextension/src/lib/mv2/background/app.ts
index 869dd775e..74ed7b1d2 100644
--- a/packages/tswebextension/src/lib/mv2/background/app.ts
+++ b/packages/tswebextension/src/lib/mv2/background/app.ts
@@ -53,6 +53,13 @@ MessageHandlerMV2
      * @returns True if app started, else false.
      */
     public get isStarted(): boolean {
+        // TODO: Remove this check after moving call of storage initialization in extension code.
+        // Check this flag before access storage values, because engine methods
+        // can be triggered before initialization by extension `onCheckRequestFilterReady` method.
+        if (!appContext.isStorageInitialized) {
+            return false;
+        }
+
         return appContext.isAppStarted;
     }
 
diff --git a/packages/tswebextension/src/lib/mv2/background/engine-api.ts b/packages/tswebextension/src/lib/mv2/background/engine-api.ts
index f2bccd1ba..d6cb60c68 100644
--- a/packages/tswebextension/src/lib/mv2/background/engine-api.ts
+++ b/packages/tswebextension/src/lib/mv2/background/engine-api.ts
@@ -48,6 +48,7 @@ export class EngineApi {
      * @returns True if filtering is enabled, otherwise returns false.
      */
     public get isFilteringEnabled(): boolean {
+        // TODO: Remove this check after moving call of storage initialization in extension code.
         // Check this flag before access storage values, because engine methods
         // can by triggered before initialization by content script requests.
         if (!this.appContext.isStorageInitialized) {