diff --git a/rules/config b/rules/config
index 3af8e706e0f..d1fc669ab58 100644
--- a/rules/config
+++ b/rules/config
@@ -185,7 +185,6 @@ SONIC_VERSION_CONTROL_COMPONENTS ?= none
 
 # SONiC docker registry
 #
-# Uncomment below line to enable pulling sonic-slave docker from registry
-# ENABLE_DOCKER_BASE_PULL = y
-REGISTRY_PORT=443
-REGISTRY_SERVER=sonicdev-microsoft.azurecr.io
+# Set the env variable ENABLE_DOCKER_BASE_PULL = y to enable pulling sonic-slave docker from registry
+REGISTRY_PORT ?= 443
+REGISTRY_SERVER ?= sonicdev-microsoft.azurecr.io