diff --git a/packages/runtime-core/src/apiWatch.ts b/packages/runtime-core/src/apiWatch.ts
index d840864454f..2775d9002b0 100644
--- a/packages/runtime-core/src/apiWatch.ts
+++ b/packages/runtime-core/src/apiWatch.ts
@@ -190,6 +190,14 @@ function doWatch(
     }
   }
 
+  // TODO remove in 3.5
+  if (__DEV__ && deep !== void 0 && typeof deep === 'number') {
+    warn(
+      `watch() "deep" option with number value will be used as watch depth in future versions. ` +
+        `Please use a boolean instead to avoid potential breakage.`,
+    )
+  }
+
   if (__DEV__ && !cb) {
     if (immediate !== undefined) {
       warn(