diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index f89f07c9580e..9ac1fc2ed05b 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -3403,7 +3403,7 @@ int dbExtendFS(struct inode *ipbmap, s64 blkno,	s64 nblocks)
 	oldl2agsize = bmp->db_agl2size;
 
 	bmp->db_agl2size = l2agsize;
-	bmp->db_agsize = 1 << l2agsize;
+	bmp->db_agsize = (s64)1 << l2agsize;
 
 	/* compute new number of AG */
 	agno = bmp->db_numag;