diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index f0555c083617671dae21b17ecb98cb3a22da3651..07b81097b84f557bebcebe2baa1f2cff4246d0b2 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -3470,7 +3470,7 @@ 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;