diff --git a/tz.h b/tz.h
index 9b8f4d7..ec80235 100644
--- a/tz.h
+++ b/tz.h
@@ -1131,7 +1131,7 @@ inline
 std::basic_ostream<CharT, Traits>&
 operator<<(std::basic_ostream<CharT, Traits>& os, const zoned_time<Duration>& t)
 {
-    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', CharT{}};
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', ' ', '%', 'Z', CharT{}};
     return to_stream(os, fmt, t);
 }