diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 4e6498c..2ceed43 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,4 +1,5 @@
-image: ruby:2.5-alpine
+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
 
 build site:
   stage: build
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..53e5a81
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "tango"]
+    path = themes/tango
+    url = ../hugo-tango-theme.git