diff --git a/compose.extra_env.yml b/compose.extra_env.yml
new file mode 100644
index 0000000..d0132ee
--- /dev/null
+++ b/compose.extra_env.yml
@@ -0,0 +1,7 @@
+---
+version: "3.8"
+
+services:
+  app:
+    environment:
+      - FOO=bar