diff --git a/Dockerfile b/Dockerfile
index 48dc497..1453220 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,7 @@
 ARG LAB_IMAGE=jupyter/datascience-notebook:lab-3.5.2
 
 FROM ${LAB_IMAGE}
+RUN echo "install custom extensions"
 RUN pip install --extra-index-url https://git.sandbox.iuk.hdm-stuttgart.de/api/packages/grosse/pypi/simple jupyterlab-sandbox-theme
 RUN pip install --extra-index-url https://git.sandbox.iuk.hdm-stuttgart.de/api/packages/grosse/pypi/simple jupyterlab-data-pool
 RUN pip install --extra-index-url https://git.sandbox.iuk.hdm-stuttgart.de/api/packages/grosse/pypi/simple jupyterlab-training