diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 3e1dd66bd6769b76d17fd1c8b7ad8da75c1b1c00..e54f5aed30a9b302aa16c6f54664a74688b6917f 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -869,6 +869,7 @@ xfs_alloc_file_space(
 	xfs_filblks_t		allocatesize_fsb;
 	xfs_extlen_t		extsz, temp;
 	xfs_fileoff_t		startoffset_fsb;
+	xfs_fileoff_t		endoffset_fsb;
 	int			nimaps;
 	int			quota_flag;
 	int			rt;
@@ -896,7 +897,8 @@ xfs_alloc_file_space(
 	imapp = &imaps[0];
 	nimaps = 1;
 	startoffset_fsb	= XFS_B_TO_FSBT(mp, offset);
-	allocatesize_fsb = XFS_B_TO_FSB(mp, count);
+	endoffset_fsb = XFS_B_TO_FSB(mp, offset + count);
+	allocatesize_fsb = endoffset_fsb - startoffset_fsb;
 
 	/*
 	 * Allocate file space until done or until there is an error