diff --git a/src/osg/GLExtensions.cpp b/src/osg/GLExtensions.cpp
index 7752eaa25..cfa08f90d 100644
--- a/src/osg/GLExtensions.cpp
+++ b/src/osg/GLExtensions.cpp
@@ -14,6 +14,7 @@
 #include <osg/GL>
 #include <osg/GLU>
 #include <osg/Notify>
+#include <osg/Math>
 #include <osg/buffered_value>
 
 #include <stdlib.h>