diff --git a/src/osg/ContextData.cpp b/src/osg/ContextData.cpp
index c33c4adfc..bdbc4aaf6 100644
--- a/src/osg/ContextData.cpp
+++ b/src/osg/ContextData.cpp
@@ -25,7 +25,8 @@ static OpenThreads::ReentrantMutex s_contextIDMapMutex;
 static ContextData::GraphicsContexts s_registeredContexts;
 
 ContextData::ContextData(unsigned int contextID):
-    GraphicsObjectManager("ContextData", contextID)
+    GraphicsObjectManager("ContextData", contextID),
+    _numContexts(0)
 {
 }