Index: /trunk/build.xml
===================================================================
--- /trunk/build.xml	(revision 17546)
+++ /trunk/build.xml	(revision 17547)
@@ -479,5 +479,5 @@
 	                    <jvmarg value="--add-opens" if:set="isJava9" />
 	                    <jvmarg value="java.desktop/java.awt=ALL-UNNAMED" if:set="isJava9" />
-                        <jvmarg value="-XX:+ShowCodeDetailsInExceptionMessages" if:set="isJava14" />
+                        <jvmarg value="-XX:+ShowCodeDetailsInExceptionMessages" if:set="isJava14" unless:set="isJava15" />
 	                    <sysproperty key="josm.home" value="${test.dir}/config/@{testfamily}-josm.home"/>
 	                    <sysproperty key="josm.test.data" value="${test.dir}/data"/>