diff --git a/.yarnrc b/.yarnrc
new file mode 100644
index 000000000..6b325e41e
--- /dev/null
+++ b/.yarnrc
@@ -0,0 +1,4 @@
+# package.json pins one Node version in "engines" so Heroku builds fetch that
+# exact one. Don't make yarn refuse to install on any other Node: CI and
+# contributors run their own.
+ignore-engines true