Index: head/sys/fs/tmpfs/tmpfs_subr.c
===================================================================
--- head/sys/fs/tmpfs/tmpfs_subr.c
+++ head/sys/fs/tmpfs/tmpfs_subr.c
@@ -218,6 +218,8 @@
 		 */
 		return (EBUSY);
 	}
+	if ((mp->mnt_kern_flag & MNT_RDONLY) != 0)
+		return (EROFS);
 
 	nnode = (struct tmpfs_node *)uma_zalloc_arg(tmp->tm_node_pool, tmp,
 	    M_WAITOK);