diff --git a/Dockerfile b/Dockerfile
index 0879e25..826fc40 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -18,7 +18,7 @@ RUN composer self-update
 # Remove the old hello world app and grab Mediawiki source
 RUN apt-get update && apt-get install -yq git && rm -rf /var/lib/apt/lists/*
 RUN rm -fr /app && mv /var/www/html /var/www/w && git clone https://gerrit.wikimedia.org/r/p/mediawiki/core.git /app
-RUN cd /app && git checkout -b $MW_VERSION origin/$MW_VERSION
+RUN cd /app && git checkout -b $MW_VERSION origin/$MW_VERSION && git submodule update --init
 
 # Install extensions
 ADD add_extension.sh /add_extension.sh