diff --git a/js/xpconnect/src/dombindings.cpp b/js/xpconnect/src/dombindings.cpp
index 630c7f067bc..daa7834a95e 100644
--- a/js/xpconnect/src/dombindings.cpp
+++ b/js/xpconnect/src/dombindings.cpp
@@ -956,9 +956,10 @@ ListBase<LC>::iterate(JSContext *cx, JSObject *proxy, unsigned flags, Value *vp)
 
 template<class LC>
 bool
-ListBase<LC>::hasInstance(JSContext *cx, JSObject *proxy, const Value *vp, bool *bp)
+ListBase<LC>::hasInstance(JSContext *cx, JS::HandleObject proxy, JS::MutableHandleValue vp,
+                          bool *bp)
 {
-    *bp = vp->isObject() && js::GetObjectClass(&vp->toObject()) == &sInterfaceClass;
+    *bp = vp.isObject() && js::GetObjectClass(&vp.toObject()) == &sInterfaceClass;
     return true;
 }
 
diff --git a/js/xpconnect/src/dombindings.h b/js/xpconnect/src/dombindings.h
index e3bae620f7c..040a963fdea 100644
--- a/js/xpconnect/src/dombindings.h
+++ b/js/xpconnect/src/dombindings.h
@@ -180,7 +180,7 @@ public:
     bool iterate(JSContext *cx, JSObject *proxy, unsigned flags, JS::Value *vp);
 
     /* Spidermonkey extensions. */
-    bool hasInstance(JSContext *cx, JSObject *proxy, const JS::Value *vp, bool *bp);
+    bool hasInstance(JSContext *cx, JS::HandleObject proxy, JS::MutableHandleValue vp, bool *bp);
     JSString *obj_toString(JSContext *cx, JSObject *proxy);
     void finalize(JSFreeOp *fop, JSObject *proxy);