Thanks for the heads-up. Although we got the most-important thing right (the UTC offset), we got a few details wrong for Yukon. We guessed that Yukon's rule change took effect March 8 which meant that since then Yukon observed standard-time (-07), which we use "MST" as an abbreviation for, with tm_isdst == 0. But the act officially takes effect November 1, which means timestamps between March 8 and November 1 should follow the old rules and use "PDT" as an abbreviation, with tm_isdst == 1. Most users won't care about this discrepancy as they see neither the alphabetic abbreviations nor tm_isdst, but for the few who do care I installed the attached proposed patch. I suppose we should put out a new tzdb release reasonably soon because of this, as current timestamps have the "wrong" labels in Yukon.