diff --git a/src/osgUtil/Simplifier.cpp b/src/osgUtil/Simplifier.cpp
index c3339a45e..5090d870b 100644
--- a/src/osgUtil/Simplifier.cpp
+++ b/src/osgUtil/Simplifier.cpp
@@ -812,8 +812,11 @@ public:
         }
 
         //osg::notify(osg::NOTICE)<<"  pNew="<<pNew<<"\tedge_p1"<<edge_p1.get()<<"\tedge_p2"<<edge_p2.get()<<std::endl;
-        for(TriangleSet::iterator teitr=edge->_triangles.begin();
-            teitr!=edge->_triangles.end();
+        
+        // we copy the edge's _triangles to and interate the copy of the triangle set to avoid invalidating iterators.
+        TriangleSet trianglesToRemove = edge->_triangles;
+        for(TriangleSet::iterator teitr=trianglesToRemove.begin();
+            teitr!=trianglesToRemove.end();
             ++teitr)
         {
             Triangle* triangle = const_cast<Triangle*>(teitr->get());