Duplicate entries in aggregate report

<build>
    ...
    <plugins>
        ...
        <plugin>
      	    <groupId>org.apache.maven.plugins</groupId>
      	    <artifactId>maven-site-plugin</artifactId>
      	    <version>3.0</version>
      	    <configuration>
      	    <reportPlugins>
                ...
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-checkstyle-plugin</artifactId>
                    <version>2.9.1</version>
                    <configuration>
                        <configLocation>checkstyle.xml</configLocation>
                        <includeTestSourceDirectory>true</includeTestSourceDirectory>
                    </configuration>
                    <reports>
                      <report>checkstyle-aggregate</report>
                    </reports>
                </plugin>
                ...
            </reportPlugins>
        </configuration>
      </plugin>
    ...
    </plugins>
    ...
</build>