Index: sys/kern/kern_jail.c
===================================================================
--- sys/kern/kern_jail.c	(revision 292065)
+++ sys/kern/kern_jail.c	(working copy)
@@ -1580,11 +1580,14 @@
 #endif
 	onamelen = namelen = 0;
 	if (name != NULL) {
-		/* Give a default name of the jid. */
+		/* Give a default name of the jid.  Also allow the name to be
+		 * explicitly the jid - but not any other number, and only in
+		 * normal form (no leading space/zero/etc).
+		 */
 		if (name[0] == '\0')
 			snprintf(name = numbuf, sizeof(numbuf), "%d", jid);
-		else if (*namelc == '0' || (strtoul(namelc, &p, 10) != jid &&
-		    *p == '\0')) {
+		else if ((strtoul(namelc, &p, 10) != jid ||
+			  namelc[0] < '1' || namelc[0] > '9') && *p == '\0') {
 			error = EINVAL;
 			vfs_opterror(opts,
 			    "name cannot be numeric (unless it is the jid)");