diff --git a/sys/kern/vfs_conf.c b/sys/kern/vfs_conf.c
--- a/sys/kern/vfs_conf.c
+++ b/sys/kern/vfs_conf.c
@@ -427,7 +427,7 @@
 		strncpy(mf, cp, MFSNAMELEN+MNAMELEN);
 
 		vfsname[0] = devname[0] = 0;
-		ksprintf(patt, "%%%d[a-z0-9]:%%%ds", MFSNAMELEN, MNAMELEN);
+		ksprintf(patt, "%%%d[a-z0-9]:%%%ds", MFSNAMELEN - 1, MNAMELEN - 1);
 		if (ksscanf(mf, patt, vfsname, devname) < 1)
 			goto end;