diff --git a/include/epoxy/glx.h b/include/epoxy/glx.h
index 6d41c26..3ef1dfc 100644
--- a/include/epoxy/glx.h
+++ b/include/epoxy/glx.h
@@ -30,11 +30,12 @@
 #ifndef EPOXY_GLX_H
 #define EPOXY_GLX_H
 
-#if defined(GLX_H) || defined(__glxext_h_)
+#if defined(GLX_H) || defined(__glx_h__) || defined(__glxext_h_)
 #error "epoxy/glx.h" must be included before (or in place of) "GL/glx.h".
 #endif
 
 #define GLX_H
+#define __glx_h__
 #define __glxext_h_
 
 #include "epoxy/gl.h"