diff --git a/t/Dockerfile b/t/Dockerfile
index 86abeaa..701e8b4 100644
--- a/t/Dockerfile
+++ b/t/Dockerfile
@@ -5,10 +5,14 @@ FROM docker.mgm.sipwise.com/sipwise-buster:latest
 # is updated with the current date. It will force refresh of all
 # of the base images and things like `apt-get update` won't be using
 # old cached versions when the Dockerfile is built.
-ENV REFRESHED_AT 2019-06-27
+ENV REFRESHED_AT 2019-06-28
 
-RUN apt-get update
-RUN apt-get install --assume-yes git abi-compliance-checker
+RUN apt-get update && \
+    apt-get install --assume-yes \
+      abi-compliance-checker \
+      git \
+      && \
+    apt-get clean
 
 RUN echo './t/testrunner' >>/root/.bash_history