I confirmed today at work on a Linux server that there is a problem similar to Asia/Baku, for timezone Europe/Warsaw in 1944. This is a fraction of the output produced for timezone Europe/Warsaw using JodaTime: UTC: 1944-04-03T00:59:59.000Z, Europe/Warsaw: 1944-04-03T01:59:59.000+01:00 UTC: 1944-04-03T01:00:00.000Z, Europe/Warsaw: 1944-04-03T03:00:00.000+02:00 UTC: 1944-09-30T21:59:59.000Z, Europe/Warsaw: 1944-09-30T23:59:59.000+02:00 UTC: 1944-09-30T22:00:00.000Z, Europe/Warsaw: 1944-09-30T23:00:00.000+01:00 The equivalent in zdump should be something like: Europe/Warsaw Mon Apr 3 00:59:59 1944 UTC = Mon Apr 3 01:59:59 1944 CET isdst=0 Europe/Warsaw Mon Apr 3 01:00:00 1944 UTC = Mon Apr 3 03:00:00 1944 CEST isdst=1 Europe/Warsaw Sat Sep 30 21:59:59 1944 UTC = Sat Sep 30 23:59:59 1944 CEST isdst=1 Europe/Warsaw Sat Sep 30 22:00:00 1944 UTC = Sat Sep 30 23:00:00 1944 CET isdst=0 The error is the change from DST to standard time in 1944. It should have been October 4.th. at 2:00 and not at the exact time that there is a change rule from C-Eur to Poland, which *is* the October 1.st 1944 at 0:00, but this should not result in a change in GMT offset from +2 to +1. Here is the relevant lines from the tz database source, I'm suggesting to add a line for DST for Poland rule before 1.st. October and copied a line from the C-Eur rule for convenience, but there must be many ways to do this: Rule C-Eur 1944 only - Apr 3 2:00s 1:00 S # Whitman gives 1944 Oct 7; go with Shanks. Rule C-Eur 1944 only - Oct 2 2:00s 0 - # Poland # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule Poland 1918 1919 - Sep 16 2:00s 0 - Rule Poland 1919 only - Apr 15 2:00s 1:00 S +Rule Poland 1944 only - Apr 3 2:00s 1:00 S # Whitman gives 1944 Nov 30; go with Shanks. Rule Poland 1944 only - Oct 4 2:00 0 - # For 1944-1948 Whitman gives the previous day; go with Shanks. Rule Poland 1945 only - Apr 29 0:00 1:00 S Rule Poland 1945 only - Nov 1 0:00 0 - This should produce the following zdump output: Europe/Warsaw Mon Apr 3 00:59:59 1944 UTC = Mon Apr 3 01:59:59 1944 CET isdst=0 Europe/Warsaw Mon Apr 3 01:00:00 1944 UTC = Mon Apr 3 03:00:00 1944 CEST isdst=1 Europe/Warsaw Tue Oct 3 23:59:59 1944 UTC = Wed Oct 4 01:59:59 1944 CEST isdst=1 Europe/Warsaw Wed Oct 4 00:00:00 1944 UTC = Wed Oct 4 01:00:00 1944 CET isdst=0 Jesper Nørgaard Welen Email: jnorgard@Prodigy.Net.mx Project Leader (Líder de Proyecto) Software CIMMYT - Centro Internacional de Mejoramiento de Maíz y Trigo Dirección: CIMMYT Int. c/o Jesper Nørgaard Km. 45, Carretera México-Veracruz El Batán Texcoco, Edo. de México CP 56130 MEXICO Tel.: +52 (55) 58-04-20-04 ext. 1374 Fax: +52 (55) 58-04-75-58 Tel. Casa: 53-10-05-95 ó 53-10-97-78 Download the free program World Time Explorer, I made: http://www.worldtimeexplorer.com/index.html