diff --git a/mainline/alpine-slim/Dockerfile b/mainline/alpine-slim/Dockerfile
index 11a27aa3..fe69b5a2 100644
--- a/mainline/alpine-slim/Dockerfile
+++ b/mainline/alpine-slim/Dockerfile
@@ -3,7 +3,7 @@
 #
 # PLEASE DO NOT EDIT IT DIRECTLY.
 #
-FROM alpine:3.20
+FROM alpine:3.21
 
 LABEL maintainer="NGINX Docker Maintainers <docker-maint@nginx.com>"
 
diff --git a/update.sh b/update.sh
index 8eebd74e..9a0e2cb4 100755
--- a/update.sh
+++ b/update.sh
@@ -55,7 +55,7 @@ declare -A debian=(
 )
 
 declare -A alpine=(
-    [mainline]='3.20'
+    [mainline]='3.21'
     [stable]='3.20'
 )