diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index e678fa517cf7e93a280e26a495b40b2f895667c0..2bbdae936076cc35ccf3b9d7c6ebd87689283c79 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1694,6 +1694,8 @@ 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 */