diff --git a/lustre/utils/mount_lustre.c b/lustre/utils/mount_lustre.c
index fd9ce0f01c98e2105986e366584ef1e7df8eaafe..247932cdae8648daa6c4d5a9da8c0a03c8b0dfe4 100644
--- a/lustre/utils/mount_lustre.c
+++ b/lustre/utils/mount_lustre.c
@@ -37,6 +37,7 @@
 #include "obdctl.h"
 #include <lustre_ver.h>
 #include <glob.h>
+#include <ctype.h>
 
 #define MAX_HW_SECTORS_KB_PATH  "queue/max_hw_sectors_kb"
 #define MAX_SECTORS_KB_PATH     "queue/max_sectors_kb"