diff --git a/src/core/observer/index.ts b/src/core/observer/index.ts
index 84744dd85f9..05cf69a27d8 100644
--- a/src/core/observer/index.ts
+++ b/src/core/observer/index.ts
@@ -191,7 +191,12 @@ export function defineReactive(
       } else if (getter) {
         // #7981: for accessor properties without setter
         return
-      } else if (isRef(value) && !isRef(newVal)) {
+      } else if (
+        !shallow &&
+        !isReadonly(newVal) &&
+        isRef(value) &&
+        !isRef(newVal)
+      ) {
         value.value = newVal
         return
       } else {