Log4J; how to ensure timestamps are always in GMT using ConversionPattern?

How can I ensure that all timestamps that my log4j is using, are in GMT?

I have tried the following but it prints "GMT" inside the timestamp

log4j.appender.ConversionPattern=%d{HH\:mm\:ss,SSS}{GMT} %-4r %-5p [%t] %3x - %m%n