use GL_GLEXT_PROTOTYPES
diff --git a/progs/demos/isosurf.c b/progs/demos/isosurf.c
index 1ee738d..555757c 100644
--- a/progs/demos/isosurf.c
+++ b/progs/demos/isosurf.c
@@ -33,9 +33,8 @@
 #include <windows.h>
 #undef CLIP_MASK
 #endif
-#define GL_GLEXT_LEGACY
+#define GL_GLEXT_PROTOTYPES
 #include "GL/glut.h"
-#include "GL/glext.h"
 
 #include "readtex.c"   /* I know, this is a hack.  KW: me too. */
 #define TEXTURE_FILE "../images/reflect.rgb"