diff --git a/src/osgViewer/CompositeViewer.cpp b/src/osgViewer/CompositeViewer.cpp
index b0c3236c1..530ca4e04 100644
--- a/src/osgViewer/CompositeViewer.cpp
+++ b/src/osgViewer/CompositeViewer.cpp
@@ -44,6 +44,7 @@ void CompositeViewer::constructorInit()
     _keyEventSetsDone = osgGA::GUIEventAdapter::KEY_Escape;
     _quitEventSetsDone = true;
     _threadingModel = ThreadPerContext;
+    _threadsRunning = false;
     _endBarrierPosition = AfterSwapBuffers;
     _numThreadsOnBarrier = 0;
     _startTick = 0;