diff --git a/include/osgViewer/api/X11/GraphicsWindowX11 b/include/osgViewer/api/X11/GraphicsWindowX11
index 15475dafa..f226300e4 100644
--- a/include/osgViewer/api/X11/GraphicsWindowX11
+++ b/include/osgViewer/api/X11/GraphicsWindowX11
@@ -25,6 +25,7 @@
 
 #include <X11/X.h>
 #include <GL/glx.h>
+#include <string.h>
 
 namespace osgViewer
 {