diff --git a/src/type.ts b/src/type.ts
index b81fb78d..9fd83b35 100644
--- a/src/type.ts
+++ b/src/type.ts
@@ -1,4 +1,5 @@
 import { StateTree, SubscriptionCallback } from 'pinia'
+import { UnwrapRef } from 'vue'
 
 export interface IStorage {
   getItem: (key: string) => any | Promise<any>
@@ -47,7 +48,7 @@ export interface CommonOptions<S extends StateTree = StateTree> {
    *
    * @default (state, savedState) => savedState
    */
-  merge?: (state: S, savedState: S) => S
+  merge?: (state: S, savedState: UnwrapRef<S>) => UnwrapRef<S>
 
   /**
    * When rehydrating, overwrite initial state (patch otherwise).
diff --git a/tests/index.test.ts b/tests/index.test.ts
index 5e30d43a..34e739b5 100644
--- a/tests/index.test.ts
+++ b/tests/index.test.ts
@@ -298,7 +298,7 @@ describe('hydrate', () => {
       {
         persistedState: {
           merge: (state, savedState) => {
-            return { values: [...state.values, ...savedState.values] }
+            return { values: [...state.values.value, ...savedState.values] }
           },
         },
       },