Index: /applications/editors/josm/plugins/build-common.xml
===================================================================
--- /applications/editors/josm/plugins/build-common.xml	(revision 33330)
+++ /applications/editors/josm/plugins/build-common.xml	(revision 33331)
@@ -484,4 +484,6 @@
                 <junit printsummary="yes" fork="true" forkmode="once" dir="${basedir}">
                     <jvmarg value="-Dfile.encoding=UTF-8"/>
+                    <jvmarg value="--add-opens" if:set="isJava9" />
+                    <jvmarg value="java.base/java.lang.reflect=ALL-UNNAMED" if:set="isJava9" />
                     <sysproperty key="josm.home" value="../00_core_test_config/unit-josm.home"/>
                     <sysproperty key="josm.test.data" value="${plugin.test.dir}/data"/>