diff --git a/Dockerfile.gitlabci b/Dockerfile.gitlabci
index 6655b404f..31a5093b3 100644
--- a/Dockerfile.gitlabci
+++ b/Dockerfile.gitlabci
@@ -1,5 +1,9 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
-FROM debian:unstable
+
+# This is an IaC pattern called "reheating a server template".
+# This is very fast but can accumulate cruft over time.
+# Use debian:unstable if you want to build a fresh image.
+FROM registry.salsa.debian.org/freedombox-team/plinth:gitlabci
 
 USER root
 COPY . /plinth