diff --git a/.github/workflows/docker-portability-custom.yml b/.github/workflows/docker-portability-custom.yml
index 2f21c25..d0c598b 100644
--- a/.github/workflows/docker-portability-custom.yml
+++ b/.github/workflows/docker-portability-custom.yml
@@ -9,6 +9,12 @@ on:
         type: string
         default: "dev"
 
+      ubuntu_codename:
+        description: "Ubuntu codename"
+        required: true
+        type: string
+        default: "jammy"
+
       boost_ver:
         description: "Boost version"
         required: true
diff --git a/Dockerfile.custom b/Dockerfile.custom
index 800d44c..6b02af4 100755
--- a/Dockerfile.custom
+++ b/Dockerfile.custom
@@ -1,5 +1,5 @@
 # Build the image:
-# docker build -f Dockerfile.custom --build-arg BOOST=1.74.0 ... -t chaste/runner:custom .
+# docker build -f Dockerfile.custom --build-arg BASE=jammy --build-arg BOOST=1.74.0 ... -t chaste/runner:custom .
 
 # Run the container in interactive mode:
 # docker run --init -it -e RUNNER_OFF=1 chaste/runner:custom /bin/bash
@@ -7,7 +7,9 @@
 # Run the container as a GitHub Actions runner:
 # docker run --init -it chaste/runner:custom
 
-FROM ubuntu:jammy
+ARG BASE=jammy
+
+FROM ubuntu:${BASE}
 
 ARG BOOST
 ARG HDF5