diff --git a/sbin/growfs/growfs.c b/sbin/growfs/growfs.c
index aee4c40446c..b610bd2f8c8 100644
--- a/sbin/growfs/growfs.c
+++ b/sbin/growfs/growfs.c
@@ -1567,9 +1567,9 @@ main(int argc, char **argv)
 	testbuf = malloc(sblock.fs_fsize);
 	if (testbuf == NULL)
 		err(1, "malloc");
-	rdfs((ufs2_daddr_t)((size / DEV_BSIZE) - sblock.fs_fsize),
+	rdfs((ufs2_daddr_t)((size - sblock.fs_fsize) / DEV_BSIZE),
 	    sblock.fs_fsize, testbuf, fsi);
-	wtfs((ufs2_daddr_t)((size / DEV_BSIZE) - sblock.fs_fsize),
+	wtfs((ufs2_daddr_t)((size - sblock.fs_fsize) / DEV_BSIZE),
 	    sblock.fs_fsize, testbuf, fso, Nflag);
 	free(testbuf);