--- a/js/src/vm/Watchtower.cpp
+++ b/js/src/vm/Watchtower.cpp
@@ -50,20 +50,26 @@ static bool InvokeWatchtowerCallback(JSC
 
   RootedValue rval(cx);
   return JS_CallFunctionValue(cx, nullptr, funVal, HandleValueArray(argv),
                               &rval);
 }
 
 static bool ReshapeForShadowedProp(JSContext* cx, HandleNativeObject obj,
                                    HandleId id) {
+  // |obj| has been used as the prototype of another object. Check if we're
+  // shadowing a property on its proto chain. In this case we need to reshape
+  // that object for shape teleporting to work correctly.
+  //
+  // See also the 'Shape Teleporting Optimization' comment in jit/CacheIR.cpp.
+
   MOZ_ASSERT(obj->isUsedAsPrototype());
 
   // Lookups on integer ids cannot be cached through prototypes.
-  if (JSID_IS_INT(id)) {
+  if (id.isInt()) {
     return true;
   }
 
   RootedObject proto(cx, obj->staticPrototype());
   while (proto) {
     // Lookups will not be cached through non-native protos.
     if (!proto->is<NativeObject>()) {
       break;
@@ -79,21 +85,16 @@ static bool ReshapeForShadowedProp(JSCon
   return true;
 }
 
 // static
 bool Watchtower::watchPropertyAddSlow(JSContext* cx, HandleNativeObject obj,
                                       HandleId id) {
   MOZ_ASSERT(watchesPropertyAdd(obj));
 
-  // If |obj| is a prototype of another object, check if we're shadowing a
-  // property on its proto chain. In this case we need to reshape that object
-  // for shape teleporting to work correctly.
-  //
-  // See also the 'Shape Teleporting Optimization' comment in jit/CacheIR.cpp.
   if (obj->isUsedAsPrototype()) {
     if (!ReshapeForShadowedProp(cx, obj, id)) {
       return false;
     }
   }
 
   if (MOZ_UNLIKELY(obj->useWatchtowerTestingCallback())) {
     RootedValue val(cx, IdToValue(id));