diff --git a/auto/src/glxew_head.h b/auto/src/glxew_head.h
index 2276259..88632e5 100644
--- a/auto/src/glxew_head.h
+++ b/auto/src/glxew_head.h
@@ -5,9 +5,13 @@
 #ifdef __glxext_h_
 #error glxext.h included before glxew.h
 #endif
+#ifdef GLX_H
+#error glx.h included before glxew.h
+#endif
 
 #define __glxext_h_
 #define __GLX_glx_h__
+#define GLX_H
 
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>