diff --git a/config/checkstyle/checkstyle.xml b/config/checkstyle/checkstyle.xml
index bd06ab9..429635d 100644
--- a/config/checkstyle/checkstyle.xml
+++ b/config/checkstyle/checkstyle.xml
@@ -174,7 +174,7 @@
       <property name="option" value="nl"/>
     </module>
     <module name="PackageName">
-      <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]*)*$"/>
+      <property name="format" value="^[a-z_]+(\.[a-z_][a-z0-9_]*)*$"/>
       <message key="name.invalidPattern"
              value="Package name ''{0}'' must match pattern ''{1}''."/>
     </module>