diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..f967a0f
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "mediawiki-php-wikidiff2"]
+	path = mediawiki-php-wikidiff2
+	url = git@github.com:wikimedia/mediawiki-php-wikidiff2.git
diff --git a/README.md b/README.md
index a42bbda..1894c44 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,9 @@
 # pywikidiff2
 
-Python module providing interface to wikidiff2 for SOTA wikitext diffs.
\ No newline at end of file
+Python module providing interface to wikidiff2 for SOTA wikitext diffs.
+
+# Building
+
+This is a thin wrapper around the wikidiff2 source code. If you didn't already run `git clone --recursive ...` when you cloned this repository, run
+
+`git submodule update --recursive`.
diff --git a/mediawiki-php-wikidiff2 b/mediawiki-php-wikidiff2
new file mode 160000
index 0000000..8639762
--- /dev/null
+++ b/mediawiki-php-wikidiff2
@@ -0,0 +1 @@
+Subproject commit 8639762681cb05aabb644743fee715fabe1263d4