diff --git a/cli/spdxtool/util.c b/cli/spdxtool/util.c
index 0cc484a..a0d0e8a 100644
--- a/cli/spdxtool/util.c
+++ b/cli/spdxtool/util.c
@@ -216,7 +216,7 @@ spdxtool_util_get_iso8601_time(time_t *wanted_time)
 	}
 
 	/* ISO8061 time with Z at the end */
-	strftime(buf, 21, "%FT%TZ", tm_info);
+	strftime(buf, 21, "%Y-%m-%dT%H:%M:%SZ", tm_info);
 	return buf;
 }