Duplicate context initialization parameter resteasy.injector.factory

My HelloWorld application, which contains one rest endpoint class that relies on RestEasy, worked fine on Glassfish 3.1.1 but fails when I move it to JBoss AS 7.

I'm not sure whether RestEasy is the actual issue or only a symptom. Through google I've found a few other users reporting the same exception but no solutions, and searches on this issue tracker haven't turned up duplicates that I could see. I originally tried with older versions of the resteasy jars (2.1.1) and saw no difference between that and 2.2.2.GA - both produce the exception below.

20:33:46,609 ERROR [org.apache.catalina.core.StandardContext] (MSC service thread 1-1) Context [/HelloWorld] startup failed due to previous errors: java.lang.IllegalArgumentException: Duplicate context initialization parameter resteasy.injector.factory
at org.apache.catalina.core.StandardContext.addParameter(StandardContext.java:2162) [jbossweb-7.0.0.CR4.jar:7.0.0.Final]
at org.jboss.as.web.deployment.JBossContextConfig.processWebMetaData(JBossContextConfig.java:289) [jboss-as-web-7.0.0.Final.jar:7.0.0.Final]
at org.jboss.as.web.deployment.JBossContextConfig.applicationWebConfig(JBossContextConfig.java:166) [jboss-as-web-7.0.0.Final.jar:7.0.0.Final]
at org.apache.catalina.startup.ContextConfig.start(ContextConfig.java:417) [jbossweb-7.0.0.CR4.jar:7.0.0.Final]
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:182) [jbossweb-7.0.0.CR4.jar:7.0.0.Final]
at org.jboss.as.web.deployment.JBossContextConfig.lifecycleEvent(JBossContextConfig.java:159) [jboss-as-web-7.0.0.Final.jar:7.0.0.Final]
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:115) [jbossweb-7.0.0.CR4.jar:7.0.0.Final]
at org.apache.catalina.core.StandardContext.start(StandardContext.java:3766) [jbossweb-7.0.0.CR4.jar:7.0.0.Final]
at org.jboss.as.web.deployment.WebDeploymentService.start(WebDeploymentService.java:70) [jboss-as-web-7.0.0.Final.jar:7.0.0.Final]
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1765)
at org.jboss.msc.service.ServiceControllerImpl$ClearTCCLTask.run(ServiceControllerImpl.java:2291)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [:1.6.0_26]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [:1.6.0_26]
at java.lang.Thread.run(Thread.java:662) [:1.6.0_26]

20:33:46,609 ERROR [org.apache.catalina.core.StandardContext] (MSC service thread 1-1) Context [/HelloWorld] startup failed due to previous errors