diff --git a/src/node.cc b/src/node.cc
index 9b27bfd5b0b..94af50941bf 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -919,6 +919,7 @@ Handle<Value> UsingDomains(const Arguments& args) {
   Local<Function> ndt = ndt_v.As<Function>();
   process->Set(String::New("_tickCallback"), tdc);
   process->Set(String::New("nextTick"), ndt);
+  process_tickCallback.Dispose();  // Possibly already set by MakeCallback().
   process_tickCallback = Persistent<Function>::New(tdc);
   return Undefined();
 }