diff --git a/src/osg/GLExtensions.cpp b/src/osg/GLExtensions.cpp
index b969340c6..93ac3dd2c 100644
--- a/src/osg/GLExtensions.cpp
+++ b/src/osg/GLExtensions.cpp
@@ -44,6 +44,8 @@ float osg::getGLVersionNumber()
 {
     // needs to be extended to do proper things with subversions like 1.5.1, etc.
     char *versionstring   = (char*) glGetString( GL_VERSION );
+    if (!versionstring) return 0.0;
+
     std::string vs( versionstring );
     return( atof( vs.substr( 0, vs.find( " " ) ).c_str() ) );
 }