diff --git a/include/osgFX/Technique b/include/osgFX/Technique
index dac5fdbeb..e0b9873eb 100644
--- a/include/osgFX/Technique
+++ b/include/osgFX/Technique
@@ -123,28 +123,32 @@ namespace osgFX
 
     private:
         typedef std::vector<osg::ref_ptr<osg::StateSet> > Pass_list;
-        Pass_list _passes;
+        OpenThreads::Mutex  _mutex;
+        OpenThreads::Atomic _passesDefined;
+        Pass_list           _passes;
     };
 
     // INLINE METHODS
 
     inline int Technique::getNumPasses() const
     {
-        return static_cast<int>(_passes.size());
+        return _passesDefined!=0 ? static_cast<int>(_passes.size()) : 0;
     }
 
     inline osg::StateSet* Technique::getPassStateSet(int i)
     {
-        return _passes[i].get();
+        return _passesDefined!=0 ? _passes[i].get() : 0;
     }
 
     inline const osg::StateSet* Technique::getPassStateSet(int i) const
     {
-        return _passes[i].get();
+        return _passesDefined!=0 ? _passes[i].get() : 0;
     }
 
     inline void Technique::dirtyPasses()
     {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock( _mutex);
+        _passesDefined.exchange(0);
         _passes.clear();
     }
 
diff --git a/src/osgFX/Technique.cpp b/src/osgFX/Technique.cpp
index 1104dadcf..adaf97aab 100644
--- a/src/osgFX/Technique.cpp
+++ b/src/osgFX/Technique.cpp
@@ -8,7 +8,8 @@
 using namespace osgFX;
 
 Technique::Technique()
-:    osg::Referenced()
+:    osg::Referenced(),
+    _passesDefined(0)
 {
 }
 
@@ -37,8 +38,16 @@ bool Technique::validate(osg::State& state) const
 void Technique::traverse_implementation(osg::NodeVisitor& nv, Effect* fx)
 {
     // define passes if necessary
-    if (_passes.empty()) {
-        define_passes();
+    if (_passesDefined==0)
+    {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock( _mutex);
+
+        if (_passesDefined==0)
+        {
+            define_passes();
+
+            _passesDefined.exchange(1);
+        }
     }
 
     // special actions must be taken if the node visitor is actually a CullVisitor
@@ -46,7 +55,7 @@ void Technique::traverse_implementation(osg::NodeVisitor& nv, Effect* fx)
     if (cv)
     {
         // traverse all passes
-        for (int i=0; i<getNumPasses(); ++i)
+        for (int i=0; i<_passes.size(); ++i)
         {
             // push the i-th pass' StateSet
             cv->pushStateSet(_passes[i].get());