diff --git a/factory/Dockerfile b/factory/Dockerfile
index e72daca77a..afb62e8750 100644
--- a/factory/Dockerfile
+++ b/factory/Dockerfile
@@ -1,5 +1,7 @@
-
-ARG FACTORY_VERSION
+# FACTORY_VERSION is expected to be overridden
+# Regular builds, using docker compose, take the value from
+# the .env file in the same directory as this file
+ARG FACTORY_VERSION='4.1.0'
 
 # Multi-stage default image. Used to test and create the pre-built docker images.
 FROM cypress/factory:${FACTORY_VERSION} AS default_image