diff --git a/Dockerfile b/Dockerfile
index 4a0bdcd..aa26b00 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -34,16 +34,20 @@
 
 COPY init.groovy /usr/share/jenkins/ref/init.groovy.d/tcp-slave-agent-port.groovy
 
+# jenkins version being bundled in this docker image
 ARG JENKINS_VERSION
 ENV JENKINS_VERSION ${JENKINS_VERSION:-2.7.1}
-ARG JENKINS_SHA
-ENV JENKINS_SHA ${JENKINS_SHA:-12d820574c8f586f7d441986dd53bcfe72b95453}
 
+# jenkins.war checksum, download will be validated using it
+ARG JENKINS_SHA=12d820574c8f586f7d441986dd53bcfe72b95453
 
-# could use ADD but this one does not check Last-Modified header 
+# Can be used to customize where jenkins.war get downloaded from
+ARG JENKINS_URL=http://repo.jenkins-ci.org/public/org/jenkins-ci/main/jenkins-war/${JENKINS_VERSION}/jenkins-war-${JENKINS_VERSION}.war
+
+# could use ADD but this one does not check Last-Modified header neither does it allow to control checksum 
 # see https://github.com/docker/docker/issues/8331
-RUN curl -fsSL http://repo.jenkins-ci.org/public/org/jenkins-ci/main/jenkins-war/${JENKINS_VERSION}/jenkins-war-${JENKINS_VERSION}.war -o /usr/share/jenkins/jenkins.war \
-  && echo "$JENKINS_SHA  /usr/share/jenkins/jenkins.war" | sha1sum -c -
+RUN curl -fsSL ${JENKINS_URL} -o /usr/share/jenkins/jenkins.war \
+  && echo "${JENKINS_SHA}  /usr/share/jenkins/jenkins.war" | sha1sum -c -
 
 ENV JENKINS_UC https://updates.jenkins.io
 RUN chown -R ${user} "$JENKINS_HOME" /usr/share/jenkins/ref