diff --git a/build.xml b/build.xml
index bd9c7de59..4fe21f424 100644
--- a/build.xml
+++ b/build.xml
@@ -534,6 +534,7 @@
         <!-- absolute paths in CLASSPATH -->
         <contains string="${java.class.path}"
                   substring="${build.tests.resolved}"/>
+        <istrue value="${junit.fork}"/>
       </or>
     </condition>