diff --git a/.ci/Dockerfile.gitlabci b/.ci/Dockerfile.gitlabci
index 867b53c28..0e22916a6 100644
--- a/.ci/Dockerfile.gitlabci
+++ b/.ci/Dockerfile.gitlabci
@@ -1,22 +1,28 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# This is an IaC pattern called "reheating a server template".
-# This is very fast but can accumulate cruft over time.
-# Use debian:testing if you want to build a fresh image.
-FROM registry.salsa.debian.org/freedombox-team/freedombox:gitlabci
+FROM debian:testing
 
 USER root
 COPY . /plinth
 WORKDIR /plinth
 
 RUN echo "deb http://deb.debian.org/debian testing main" > /etc/apt/sources.list
-RUN echo "deb-src http://deb.debian.org/debian testing main" >> /etc/apt/sources.list
 
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update
-RUN apt-get build-dep -y .  # Dependencies of the freedombox Debian package
-RUN apt-get install -y build-essential # Build dependencies
-RUN apt-get install -y sshpass parted # Test dependencies
-RUN apt-get install -y sudo
-RUN apt-get install -y $(./run --list-dependencies) # Module dependencies
+
+# Dependencies of the freedombox Debian package
+RUN apt-get build-dep -y .
+
+# Build dependencies
+RUN apt-get install -y build-essential \
+    # Test dependencies
+    sshpass parted \
+    sudo python3-pip
+
+# Module dependencies
+RUN apt-get install -y $(./run --list-dependencies)
+
+# Coverage should know that test_functional.py files are tests
+RUN pip3 install splinter pytest-bdd
diff --git a/.ci/Dockerfile.gitlabci.dockerignore b/.ci/Dockerfile.gitlabci.dockerignore
new file mode 100644
index 000000000..89ddad767
--- /dev/null
+++ b/.ci/Dockerfile.gitlabci.dockerignore
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+**/.git
+**/.container
+**/.vagrant
+**/.ci
+**/functional_tests
+**/doc
+**/build
+**/static
diff --git a/.ci/update-gitlabci-docker-image.sh b/.ci/update-gitlabci-docker-image.sh
index 4143610b9..9ada7724d 100755
--- a/.ci/update-gitlabci-docker-image.sh
+++ b/.ci/update-gitlabci-docker-image.sh
@@ -1,9 +1,8 @@
 #! /bin/bash
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# Provide your Salsa credentials here
 docker login registry.salsa.debian.org
 
-# This might need 20 minutes to run
-docker build -t registry.salsa.debian.org/freedombox-team/freedombox:gitlabci -f .ci/Dockerfile.gitlabci .
+# Build and upload a new image to the container registry
+DOCKER_BUILDKIT=1 docker build -t registry.salsa.debian.org/freedombox-team/freedombox:gitlabci -f .ci/Dockerfile.gitlabci .
 docker push registry.salsa.debian.org/freedombox-team/freedombox:gitlabci