diff --git a/pom.xml b/pom.xml
index 9568fc8..e4103fd 100644
--- a/pom.xml
+++ b/pom.xml
@@ -545,6 +545,7 @@
               </execution>
             </executions>
             <configuration>
+              <source>1.8</source>
               <tags>
                 <tag>
                   <!-- to avoid protostuff javadoc problem. -->