diff --git a/docs/custom-base-image.md b/docs/custom-base-image.md
index 00e9e888c..716c46b42 100644
--- a/docs/custom-base-image.md
+++ b/docs/custom-base-image.md
@@ -15,7 +15,7 @@ Use this template for using a custom base image with our default user named `ubu
 # This containerbase is used for tool intallation and user/directory setup
 FROM containerbase/base AS containerbase
 
-FROM amd64/ubuntu:jammy as base
+FROM amd64/ubuntu:jammy AS base
 
 # Allows custom apt proxy usage
 ARG APT_HTTP_PROXY
@@ -58,7 +58,7 @@ You can also customize username or userid by using this template.
 # This containerbase is used for tool intallation and user/directory setup
 FROM containerbase/base AS containerbase
 
-FROM amd64/ubuntu:jammy as base
+FROM amd64/ubuntu:jammy AS base
 
 # The containerbase supports custom user
 ARG USER_NAME=custom
@@ -107,7 +107,7 @@ The group must already exist.
 # This containerbase is used for tool intallation and user/directory setup
 FROM containerbase/base AS containerbase
 
-FROM amd64/ubuntu:jammy as base
+FROM amd64/ubuntu:jammy AS base
 
 ARG USER_NAME=gitpod
 ARG USER_ID=33333