diff --git a/.CI/testing/Dockerfile b/.CI/testing/Dockerfile
index 434ba0b..ed012fe 100644
--- a/.CI/testing/Dockerfile
+++ b/.CI/testing/Dockerfile
@@ -54,7 +54,9 @@ ENV PATH=/opt/libtest-venv/bin:$PATH
 
 # The omc for --ompython_omhome (the tested one is built in the workspace).
 ARG OMC_VERSION=
+ARG OMC_NIGHTLY=2026-11-11
 RUN export DEBIAN_FRONTEND=noninteractive \
+  && echo "omc nightly ${OMC_NIGHTLY}" \
   && . /etc/os-release \
   && echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/openmodelica-keyring.gpg]" \
           "https://build.openmodelica.org/apt ${VERSION_CODENAME} nightly" \