diff --git a/sys/fs/msdosfs/msdosfs_fat.c b/sys/fs/msdosfs/msdosfs_fat.c
index 4a7faa9e1f05..bfaff417f677 100644
--- a/sys/fs/msdosfs/msdosfs_fat.c
+++ b/sys/fs/msdosfs/msdosfs_fat.c
@@ -97,7 +97,7 @@ fatblock(struct msdosfsmount *pmp, u_long ofs, u_long *bnp, u_long *sizep,
 			fatblocksec /= 2;
 	}
 	bn = ofs / pmp->pm_fatblocksize * pmp->pm_fatblocksec;
-	size = roundup(min(fatblocksec, pmp->pm_FATsecs - bn) * DEV_BSIZE,
+	size = roundup(ulmin(fatblocksec, pmp->pm_FATsecs - bn) * DEV_BSIZE,
 	    pmp->pm_BlkPerSec * DEV_BSIZE);
 	bn += pmp->pm_fatblk + pmp->pm_curfat * pmp->pm_FATsecs;