diff --git a/Dockerfile b/Dockerfile
index 914d06a9..90259508 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,6 @@
 # This file is intended to be used apart from the containing source code tree.
 
-FROM python:3-alpine as builder
+FROM python:3-alpine AS builder
 
 # Version of Radicale (e.g. v3)
 ARG VERSION=master
diff --git a/Dockerfile.dev b/Dockerfile.dev
index 36ff98e5..65e00fcd 100644
--- a/Dockerfile.dev
+++ b/Dockerfile.dev
@@ -1,4 +1,4 @@
-FROM python:3-alpine as builder
+FROM python:3-alpine AS builder
 
 # Optional dependencies (e.g. bcrypt)
 ARG DEPENDENCIES=bcrypt