diff --git a/lib/ext2fs/blknum.c b/lib/ext2fs/blknum.c
index b9666fb..fd56d53 100644
--- a/lib/ext2fs/blknum.c
+++ b/lib/ext2fs/blknum.c
@@ -28,7 +28,7 @@ dgrp_t ext2fs_group_of_blk2(ext2_filsys fs, blk64_t blk)
 blk64_t ext2fs_group_first_block2(ext2_filsys fs, dgrp_t group)
 {
 	return fs->super->s_first_data_block +
-		(group * fs->super->s_blocks_per_group);
+		((blk64_t)group * fs->super->s_blocks_per_group);
 }
 
 /*