diff --git a/Makefile b/Makefile
index ebf77ac..02daeac 100644
--- a/Makefile
+++ b/Makefile
@@ -5,8 +5,8 @@ CONTAINER_RUNTIME?=$(shell which podman)
 
 # CERTBOT_IMAGE_REGISTRY_NAME
 # Defines the name of the new container to be built using several variables.
-CERTBOT_IMAGE_REGISTRY_NAME:=git.cryptic.systems
-CERTBOT_IMAGE_REGISTRY_USER:=volker.raschek
+CERTBOT_IMAGE_REGISTRY_NAME?=git.cryptic.systems
+CERTBOT_IMAGE_REGISTRY_USER?=volker.raschek
 
 CERTBOT_IMAGE_NAMESPACE?=${CERTBOT_IMAGE_REGISTRY_USER}
 CERTBOT_IMAGE_NAME:=certbot