--- a/java/build.common.xml	Wed Aug 29 03:34:33 2018 +0000
+++ b/java/build.common.xml	Thu Sep 27 23:09:30 2018 +0100
@@ -11,6 +11,15 @@
     <property name="build.src-tests.dir" value="src-tests"/>
     <property name="build.bin-tests.dir" value="bin-tests"/>
 
+    <!--
+         As of now, stx:libjava supports at most JDK 7, so force 
+         source and target Java version to 1.7 to ensure compatibility
+
+         See https://ant.apache.org/manual/javacprops.html#source
+    -->
+    <property name="ant.build.javac.source" value="1.7"/>
+    <property name="ant.build.javac.target" value="1.7"/>
+
     <property name="test.report"     value="test-results.xml"/>
     <property name="test.report.dir" value="test-results"/>