diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index f06796cad9aa..3ad0a33e0443 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -206,7 +206,8 @@ int dbMount(struct inode *ipbmap)
 	bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
 	bmp->db_agstart = le32_to_cpu(dbmp_le->dn_agstart);
 	bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);
-	if (bmp->db_agl2size > L2MAXL2SIZE - L2MAXAG) {
+	if (bmp->db_agl2size > L2MAXL2SIZE - L2MAXAG ||
+	    bmp->db_agl2size < 0) {
 		err = -EINVAL;
 		goto err_release_metapage;
 	}