diff --git a/util-linux/fdisk.c b/util-linux/fdisk.c
index bd929d88d..31a7d8076 100644
--- a/util-linux/fdisk.c
+++ b/util-linux/fdisk.c
@@ -60,7 +60,7 @@
  * _IOR rather differently */ 
 #undef _IOR
 #define _IOR(type,nr,size)      _IOC(_IOC_READ,(type),(nr),sizeof(size))
-#define BLKGETSIZE64 _IOR(0x12,114,8)  /* 8 = sizeof(u64) */
+#define BLKGETSIZE64 _IOR(0x12,114,uint64_t)
 
 /*
    fdisk.h