diff --git a/Makefile b/Makefile
index 43cb842..cb0f5c0 100644
--- a/Makefile
+++ b/Makefile
@@ -5,8 +5,8 @@ CONTAINER_RUNTIME?=$(shell which docker)
 
 # DHCPD_IMAGE_REGISTRY_NAME
 # Defines the name of the new container to be built using several variables.
-DHCPD_IMAGE_REGISTRY_NAME:=git.cryptic.systems
-DHCPD_IMAGE_REGISTRY_USER:=volker.raschek
+DHCPD_IMAGE_REGISTRY_NAME?=git.cryptic.systems
+DHCPD_IMAGE_REGISTRY_USER?=volker.raschek
 
 DHCPD_IMAGE_NAMESPACE?=${DHCPD_IMAGE_REGISTRY_USER}
 DHCPD_IMAGE_NAME:=dhcpd