diff --git a/README_Docker.md b/README_Docker.md
index f3deef88..f2b75a5a 100644
--- a/README_Docker.md
+++ b/README_Docker.md
@@ -1,5 +1,11 @@
 # Running OpenSprinkler via Docker
 
+Before trying to build the docker image, you need to download the submodules. 
+You can do it via:
+```sh
+git submodule update --recursive --init
+```
+
 ## Building the container
 From this directory, create the image: