diff --git a/packages/pinia/src/store.ts b/packages/pinia/src/store.ts
index 4cbec9f126..923c4b120b 100644
--- a/packages/pinia/src/store.ts
+++ b/packages/pinia/src/store.ts
@@ -870,6 +870,8 @@ export function defineStore<Id extends string, SS>(
   _ExtractGettersFromSetupStore<SS>,
   _ExtractActionsFromSetupStore<SS>
 >
+// improves tree shaking
+/*#__NO_SIDE_EFFECTS__*/
 export function defineStore(
   // TODO: add proper types from above
   idOrOptions: any,