diff --git a/src/osgViewer/Viewer.cpp b/src/osgViewer/Viewer.cpp
index 0f0fd37aa..cf0a9a3a7 100644
--- a/src/osgViewer/Viewer.cpp
+++ b/src/osgViewer/Viewer.cpp
@@ -26,6 +26,7 @@ Viewer::Viewer():
     _keyEventSetsDone(osgGA::GUIEventAdapter::KEY_Escape),
     _quitEventSetsDone(true),
     _threadingModel(ThreadPerContext),
+    _useMainThreadForRenderingTraversal(false),
     _endBarrierPosition(AfterSwapBuffers),
     _numThreadsOnBarrier(0)
 {