diff --git a/hooks/post_checkout b/hooks/post_checkout
new file mode 100755
index 00000000..a01590a5
--- /dev/null
+++ b/hooks/post_checkout
@@ -0,0 +1,5 @@
+#!/bin/bash
+# Docker hub does a recursive clone, then checks the branch out,
+# so when a PR adds a submodule (or updates it), it fails.
+
+git submodule update --init
diff --git a/package.json b/package.json
index 509c4915..e2adb7a9 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,8 @@
     "url": "https://github.com/ohmyform/ohmyform.git"
   },
   "engines": {
-    "yarn": "1.x"
+    "yarn": "1.x",
+    "node": "12.x"
   },
   "scripts": {
     "heroku-prebuild": "scripts/heroku/prebuild.sh",