--- a/taskcluster/docker/decision/Dockerfile
+++ b/taskcluster/docker/decision/Dockerfile
@@ -1,15 +1,16 @@
 FROM          ubuntu:16.04
-MAINTAINER    Greg Arndt <garndt@mozilla.com>
+MAINTAINER    Dustin Mitchell <dustin@mozilla.com>
 
 # Add worker user
-RUN mkdir /builds
-RUN useradd -d /builds/worker -s /bin/bash -m worker
-RUN mkdir /builds/worker/artifacts && chown worker:worker /builds/worker/artifacts
+RUN mkdir /builds && \
+    useradd -d /builds/worker -s /bin/bash -m worker && \
+    mkdir /builds/worker/artifacts && \
+    chown worker:worker /builds/worker/artifacts
 
 # %include python/mozbuild/mozbuild/action/tooltool.py
 ADD topsrcdir/python/mozbuild/mozbuild/action/tooltool.py /tmp/tooltool.py
 
 # %include testing/mozharness/external_tools/robustcheckout.py
 ADD topsrcdir/testing/mozharness/external_tools/robustcheckout.py /usr/local/mercurial/robustcheckout.py
 
 # %include taskcluster/docker/recipes/hgrc
@@ -19,14 +20,14 @@ COPY topsrcdir/taskcluster/docker/recipe
 ADD topsrcdir/taskcluster/docker/recipes/install-mercurial.sh /tmp/install-mercurial.sh
 
 ADD system-setup.sh /tmp/system-setup.sh
 RUN bash /tmp/system-setup.sh
 
 # %include taskcluster/docker/recipes/run-task
 ADD topsrcdir/taskcluster/docker/recipes/run-task /builds/worker/bin/run-task
 
-ENV PATH /builds/worker/bin:$PATH
-ENV SHELL /bin/bash
-ENV HOME /builds/worker
+ENV PATH=/builds/worker/bin:$PATH \
+    SHELL=/bin/bash \
+    HOME=/builds/worker
 
 # Set a default command useful for debugging
 CMD ["/bin/bash", "--login"]

--- a/taskcluster/docker/decision/system-setup.sh
+++ b/taskcluster/docker/decision/system-setup.sh
@@ -22,9 +22,10 @@ tooltool_fetch() {
 cd $BUILD
 # shellcheck disable=SC1091
 . /tmp/install-mercurial.sh
 
 cd /
 rm -rf $BUILD
 apt-get clean
 apt-get autoclean
+rm -rf /var/lib/apt/lists/
 rm "$0"