 Pact provided opportunity to be denounced 6 months before expiration or by either Estonia or USSR at any time without notice in the event of an act of aggression by the other party against any third state.If not denounced the pact was to be prolonged each two years for indetermined period.The pact was prolonged until 31 December 1945 on 4 April 1934 and was again reafirmed on 28 September 1939.