--- a/lib/master.cc
+++ b/lib/master.cc
@@ -409,7 +409,9 @@ Master::process_pending(RouterThread *th
     while (Task *t = Task::pending_to_task(my_pending)) {
 	my_pending = t->_pending_nextptr;
 	t->_pending_nextptr = 0;
+# if HAVE_MULTITHREAD
 	click_master_mb();
+# endif
 	t->process_pending(thread);
     }
 }