Play plugin override default http port 9000 doesn't work

We have a different app using port 9000 so we like to override the default play http port through:

tasks.withType(PlayRun) {
   forkOptions.jvmArgs  =["-Dhttp.port=7777 -Dproperties.home=conf"]  
   println " ----> forkOptions.jvmArgs = ${ forkOptions.jvmArgs }"

However, it doesn’t seem to work for the port (for the properties.home it works OK)
----> forkOptions.jvmArgs = [-Dhttp.port=7777 -Dproperties.home=conf ]

Failed to run Play Failed to bind to: /
        at org.jboss.netty.bootstrap.ServerBootstrap.bind(

Just figure out right after the post, httpPort is NOT in the the jvmargs but on its own:

tasks.withType(PlayRun) {
    httpPort = 7777