diff --git a/mbr.cc b/mbr.cc
index 08c61be..d317f52 100644
--- a/mbr.cc
+++ b/mbr.cc
@@ -7,7 +7,9 @@
   under the terms of the GNU GPL version 2, as detailed in the COPYING file. */
 
 #define __STDC_LIMIT_MACROS
+#ifndef __STDC_CONSTANT_MACROS
 #define __STDC_CONSTANT_MACROS
+#endif
 
 #include <stdio.h>
 #include <stdlib.h>