diff --git a/src/app/mod.rs b/src/app/mod.rs
index b23f231..339a632 100644
--- a/src/app/mod.rs
+++ b/src/app/mod.rs
@@ -1272,8 +1272,10 @@ mod tests {
     fn format_duration_renders_mss_and_hmmss() {
         assert_eq!(format_duration(0), "0:00");
         assert_eq!(format_duration(5), "0:05");
+        assert_eq!(format_duration(59), "0:59");
         assert_eq!(format_duration(65), "1:05");
         assert_eq!(format_duration(600), "10:00");
+        assert_eq!(format_duration(3599), "59:59");
         // Past an hour switches to h:mm:ss with zero-padded minutes/seconds.
         assert_eq!(format_duration(3600), "1:00:00");
         assert_eq!(format_duration(3661), "1:01:01");