diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cb3cda1390ad..20f6e81791c0 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1626,6 +1626,9 @@ s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
 		} else if (rc == -ENOSPC) {
 			/* search for next smaller log2 block */
 			l2nb = BLKSTOL2(nblocks) - 1;
+			if (unlikely(l2nb < 0))
+				break;
+
 			nblocks = 1LL << l2nb;
 		} else {
 			/* Trim any already allocated blocks */