diff --git a/src/engine/runtime.js b/src/engine/runtime.js
index 9fa953563..d97247e58 100644
--- a/src/engine/runtime.js
+++ b/src/engine/runtime.js
@@ -172,10 +172,10 @@ Runtime.prototype._pushThread = function (id) {
 
 /**
  * Remove a thread from the list of threads.
- * @param {!Thread} thread Thread object to remove from actives
+ * @param {?Thread} thread Thread object to remove from actives
  */
-Runtime.prototype._removeThread = function (id) {
-    var i = this.threads.indexOf(id);
+Runtime.prototype._removeThread = function (thread) {
+    var i = this.threads.indexOf(thread);
     if (i > -1) this.threads.splice(i, 1);
 };