The present invention is directed to a fitment assembly for a container. The fitment assembly includes a spout connected in fluid communication to the container, a cap sealing an end of the spout, the cap having a pierceable center, and a piercer for puncturing the cap at the pierceable center to permit fluid communication from the container through the spout and piercer. The present invention provides a seal between an annular skirt of the piercer and a circumferential wall of the cap so that when the piercer punctures the cap a seal is formed. The present invention also provides an additional means of securing the piercer to the cap utilizing the circumferential wall of the cap and the annular skirt of the piercer.