Happy leap second. In 2016i Pacific/Tongatapu changed to: (1) use numeric time zone abbreviations, and (2) observe DST from the first Sunday in November through the third Sunday in January. That is, its POSIX future rule became "<+13>-13<+14>,M11.1.0,M1.3.0/3". (1) results, under WORK_AROUND_QTBUG_53071, in zic adding a "y2038_boundary - 1" (i.e., 2038-01-19 03:14:07 +00:00) no-op transition to the end of the generated transitions. So, the Pacific/Tongatapu zoneinfo file looks like ... : 2115810000 gmtoff=46800 is_dst=F abbr="+13" 2140606800 gmtoff=50400 is_dst=T abbr="+14" 2147483647 gmtoff=50400 is_dst=T abbr="+14" When loading Pacific/Tongatapu at runtime, (2) results in tzloadbody() generating additional transitions ... : 2140606800 gmtoff=50400 is_dst=T abbr="+14" 2147259600 gmtoff=46800 is_dst=F abbr="+13" 2172661200 gmtoff=50400 is_dst=T abbr="+14" 2178709200 gmtoff=46800 is_dst=F abbr="+13" : When those generated transitions are patched onto the end of the zic transitions, we end up with ... 2115810000 gmtoff=46800 is_dst=F abbr="+13" 2140606800 gmtoff=50400 is_dst=T abbr="+14" 2147483647 gmtoff=50400 is_dst=T abbr="+14" 2172661200 gmtoff=50400 is_dst=T abbr="+14" 2178709200 gmtoff=46800 is_dst=F abbr="+13" This is wrong. The presence of the 2147483647 transition caused us to drop the 2147259600 transition. That is, we lost the shift out of DST at 2038-01-17 02:00:00 +13:00 (2038-01-16 13:00:00 +00:00). One solution would be to trim trailing, no-op transitions from the end of the zic transitions before adding the rule-generated ones. The reference implementation doesn't need them. Bradley