diff --git a/.env.sample b/.env.sample
index 9b7584a..4785602 100644
--- a/.env.sample
+++ b/.env.sample
@@ -8,6 +8,9 @@ ENTRYPOINT_CONF_VERSION=v1
 # Wordpress debugging
 WORDPRESS_DEBUG=1
 
+# If 1, composer install runs with "--prefer-source"
+DEV_MODE=1
+
 SELINUX=0
 
 # If you need to manually specify a path to (bash) abra, do it here: