diff --git a/extras/volume_id/lib/md5.c b/extras/volume_id/lib/md5.c
index 08606600666..9c4b2846445 100644
--- a/extras/volume_id/lib/md5.c
+++ b/extras/volume_id/lib/md5.c
@@ -20,7 +20,7 @@
 
 #include "md5.h"
 
-#if !(__BYTE_ORDER == __LITTLE_ENDIAN) && !(__BYTE_ORDER == __BIG_ENDIAN)
+#if !defined __BYTE_ORDER || !(__BYTE_ORDER == __LITTLE_ENDIAN) && !(__BYTE_ORDER == __BIG_ENDIAN)
 #error missing __BYTE_ORDER
 #endif