diff -up ./build.xml.tests-headless ./build.xml
--- ./build.xml.tests-headless	2013-07-04 20:42:30.000000000 +0200
+++ ./build.xml	2013-07-05 15:06:19.354441386 +0200
@@ -885,6 +885,7 @@ osname=macosx;processor=x86;processor=x8
       <sysproperty key="jna.builddir" file="${build}"/>
       <sysproperty key="jna.nativedir" file="${build.native}"/>
       <jvmarg value="${vmopt.arch}"/>
+      <jvmarg value="-Djava.awt.headless=true"/>
       <classpath><path refid="test.runpath"/></classpath>
       <formatter type="brief" usefile="false"/>
       <formatter type="xml"/>