diff --git a/include/osgParticle/ParticleProcessor b/include/osgParticle/ParticleProcessor
index c2b23913b..2a20a5255 100644
--- a/include/osgParticle/ParticleProcessor
+++ b/include/osgParticle/ParticleProcessor
@@ -171,6 +171,8 @@ namespace osgParticle
         //added- 1/17/06- bgandere@nps.edu 
         //a var to keep from doing multiple updates
         int _frameNumber;
+        
+        OpenThreads::Mutex _cullUpdatelMutex;
     };
     
     // INLINE FUNCTIONS
diff --git a/include/osgParticle/ParticleSystemUpdater b/include/osgParticle/ParticleSystemUpdater
index 5ab10886b..abf3070c2 100644
--- a/include/osgParticle/ParticleSystemUpdater
+++ b/include/osgParticle/ParticleSystemUpdater
@@ -91,6 +91,8 @@ namespace osgParticle
         //added 1/17/06- bgandere@nps.edu
         //a var to keep from doing multiple updates per frame
         int _frameNumber; 
+        
+        OpenThreads::Mutex _cullUpdatelMutex;
     };
     
     // INLINE FUNCTIONS
diff --git a/src/osgParticle/ParticleProcessor.cpp b/src/osgParticle/ParticleProcessor.cpp
index 39580b087..ee15abc0d 100644
--- a/src/osgParticle/ParticleProcessor.cpp
+++ b/src/osgParticle/ParticleProcessor.cpp
@@ -62,9 +62,10 @@ void osgParticle::ParticleProcessor::traverse(osg::NodeVisitor& nv)
         // continue only if the particle system is valid
         if (_ps.valid())
         {
-
             if (nv.getFrameStamp())
             {
+                OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_cullUpdatelMutex);
+
                 //added- 1/17/06- bgandere@nps.edu 
                 //a check to make sure we havent updated yet this frame
                 if(_frameNumber < nv.getFrameStamp()->getFrameNumber())
diff --git a/src/osgParticle/ParticleSystemUpdater.cpp b/src/osgParticle/ParticleSystemUpdater.cpp
index b76650954..75ff99a30 100644
--- a/src/osgParticle/ParticleSystemUpdater.cpp
+++ b/src/osgParticle/ParticleSystemUpdater.cpp
@@ -23,14 +23,18 @@ osgParticle::ParticleSystemUpdater::ParticleSystemUpdater(const ParticleSystemUp
 void osgParticle::ParticleSystemUpdater::traverse(osg::NodeVisitor& nv)
 {
     osgUtil::CullVisitor *cv = dynamic_cast<osgUtil::CullVisitor *>(&nv);
-    if (cv) {
+    if (cv) 
+    {
         if (nv.getFrameStamp())
         {
-          //added 1/17/06- bgandere@nps.edu 
-          //ensures ParticleSystem will only be updated once per frame
-          //regardless of the number of cameras viewing it
-          if( _frameNumber < nv.getFrameStamp()->getFrameNumber())
-          {
+
+            OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_cullUpdatelMutex);
+            
+            //added 1/17/06- bgandere@nps.edu 
+            //ensures ParticleSystem will only be updated once per frame
+            //regardless of the number of cameras viewing it
+            if( _frameNumber < nv.getFrameStamp()->getFrameNumber())
+            {
                 double t = nv.getFrameStamp()->getReferenceTime();
                 if (_t0 != -1)
                 {
@@ -44,10 +48,11 @@ void osgParticle::ParticleSystemUpdater::traverse(osg::NodeVisitor& nv)
                     }
                 }
                 _t0 = t;
-          }
-          //added- 1/17/06- bgandere@nps.edu 
-          //set frame number to the current frame number
-          _frameNumber = nv.getFrameStamp()->getFrameNumber();
+            }
+
+            //added- 1/17/06- bgandere@nps.edu 
+            //set frame number to the current frame number
+            _frameNumber = nv.getFrameStamp()->getFrameNumber();
         }
         else
         {