It seems that certain java.time.Instant instances prior to Instant.EPOCH are not equal after being serialized, then deserialized.

As you can see from this gist, serializing then deserializing an Instant one millisecond prior to the epoch (1969-12-31T23:59:59.999Z) results in an Instant 1.998 seconds earlier: 1969-12-31T23:59:58.001Z

As mentioned above, this affects only Instants with a nonzero nanos field. Instant.ofEpochMilli(-1001) is not equal after deserialization, while Instant.ofEpochMilli(1000) is equal.

Using OpenJDK8 1.8.0_202 and Jackson 2.9.8.