Mktime out of range during Python unit tests

This error is only thrown during nix-build. I can run the offending line in a Python interpreter and it works just fine.

ERROR: test_write_helpers (test_filelogger.TestFileLogger)
Traceback (most recent call last):
  File "/build/source/utest/output/", line 23, in setUp
    robottime.TIMESTAMP_CACHE = _FakeTimeCache()
  File "/build/source/utest/output/", line 13, in __init__
    self.fake = time.mktime((2006, 6, 13, 8, 37, 42, 0, 0, 1)) + 0.123
OverflowError: mktime argument out of range

The package I’m working on is here: