diff --git a/Dockerfile b/Dockerfile
index c427a2e..553cb64 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 
-FROM python:3.6-alpine
+FROM python:3.7-alpine
 
 RUN mkdir -p /var/matemat/db /var/matemat/upload
 RUN apk --update add libmagic
diff --git a/testing/Dockerfile b/testing/Dockerfile
index 94644e6..1c19268 100644
--- a/testing/Dockerfile
+++ b/testing/Dockerfile
@@ -1,11 +1,15 @@
 
-FROM debian:buster
+# There is no buster image yet and stretch doesn't have a docker package.  So let's just "upgrade" the image to buster.
+FROM python:3.7-stretch
 
-RUN useradd -d /home/matemat -m matemat
-RUN mkdir -p /var/matemat/db && chown matemat:matemat -R /var/matemat/db
-RUN mkdir -p /var/matemat/upload && chown matemat:matemat -R /var/matemat/upload
-RUN apt-get update -qy
-RUN apt-get install -y --no-install-recommends file sudo openssh-client git docker.io python3-dev python3-pip python3-coverage python3-setuptools build-essential
-RUN pip3 install wheel pycodestyle mypy
+RUN sed -re 's/stretch/buster/g' -i /etc/apt/sources.list \
+  && useradd -d /home/matemat -m matemat \
+  && mkdir -p /var/matemat/db /var/matemat/upload \
+  && chown matemat:matemat -R /var/matemat/db \
+  && chown matemat:matemat -R /var/matemat/upload \
+  && apt-get update -qy \
+  && apt-get install -y --no-install-recommends file sudo openssh-client git docker.io build-essential \
+  && python3.7 -m pip install wheel pycodestyle mypy \
+  && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /home/matemat