Per LOGBACK-262 [1], logback does not conform to ISO8601 when printing %d{ISO8601}. We're in the process of fixing this [2], but we'd like to maintain backward compatibility for log parsers that might rely on the incorrect format. We have a couple options. OPTION 1. Add a new option for %d that enables the legacy incorrect format. Deprecate it, and remove it after several releases. Examples: %d{ISO8601_OLD} %d{NOT8601} %d{OLD8601} %d{ISO8601,,old} other? OPTION 2. Force users to specify a custom date format that matches the legacy incorrect format: %d{"yyyy-MM-dd HH:mm:ss,SSS"} Please provide feedback on these options (or a new one) by June 23. Thanks, Tony [1] http://jira.qos.ch/browse/LOGBACK-262 [2] https://github.com/qos-ch/logback/pull/207