added a cast
diff --git a/progs/samples/quad.c b/progs/samples/quad.c
index 5b721a4..193850a 100644
--- a/progs/samples/quad.c
+++ b/progs/samples/quad.c
@@ -99,7 +99,7 @@
 static void CALLBACK ErrorHandler(GLenum which)
 {
 
-    fprintf(stderr, "Quad Error: %s\n", gluErrorString(which));
+    fprintf(stderr, "Quad Error: %s\n", (char *) gluErrorString(which));
 }
 
 typedef void (GLAPIENTRY *callback_t)();