diff --git a/xalan-j2.spec b/xalan-j2.spec
index 8d79d31..bd6d99b 100644
--- a/xalan-j2.spec
+++ b/xalan-j2.spec
@@ -135,6 +135,8 @@ popd
 export CLASSPATH=$(build-classpath glassfish-servlet-api)
 
 ant \
+  -Dcompiler.source=1.6 \
+  -Dcompiler.target=1.6 \
   -Djava.awt.headless=true \
   -Dapi.j2se=%{_javadocdir}/java \
   -Dbuild.xalan-interpretive.jar=build/xalan-interpretive.jar \