diff --git a/src/scheduler.cpp b/src/scheduler.cpp
--- a/src/scheduler.cpp
+++ b/src/scheduler.cpp
@@ -131,6 +131,7 @@
 }
 
 bool CScheduler::AreThreadsServicingQueue() const {
+    boost::unique_lock<boost::mutex> lock(newTaskMutex);
     return nThreadsServicingQueue;
 }