diff --git a/.gitea/workflows/docker.yml b/.gitea/workflows/docker.yml
index 41950c3..25f73be 100644
--- a/.gitea/workflows/docker.yml
+++ b/.gitea/workflows/docker.yml
@@ -67,12 +67,14 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v6
 
-      # The runner is an arm64 server, so the amd64 image is emulated. On its 6.8 kernel, recent
-      # QEMU builds segfault compiling PHP extensions (docker/buildx#3170); QEMU 8 is pinned.
+      # The runner is an arm64 server, so the amd64 image's final stage is emulated. QEMU 8.x
+      # crashes running x86_64 programs on an arm64 host (QEMU issue 2168, "QEMU internal
+      # SIGSEGV {code=MAPERR, addr=0x20}") and 10.2 segfaults on this runner too; 9.2.2 was
+      # checked on the runner's host: node, composer and install-php-extensions all run.
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3
         with:
-          image: tonistiigi/binfmt:qemu-v8.1.5
+          image: tonistiigi/binfmt:qemu-v9.2.2
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
diff --git a/Dockerfile b/Dockerfile
index d8c022a..8c7670b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,9 @@
 # ============================================
 # Stage 1: Install PHP dependencies
 # ============================================
-FROM composer:2 AS vendor
+# Built on the build machine's own platform: vendor/ is plain PHP, the same for every target, so a
+# multi-arch build runs it once and never under emulation.
+FROM --platform=$BUILDPLATFORM composer:2 AS vendor
 
 WORKDIR /app
 
@@ -21,8 +23,9 @@ RUN composer dump-autoload --optimize --no-dev
 # ============================================
 # Stage 2: Build frontend assets
 # ============================================
-# After Composer: the stylesheet and script import Livewire Material from vendor/.
-FROM node:24-alpine AS assets
+# After Composer: the stylesheet and script import Livewire Material from vendor/. On the build
+# machine's platform too: the output is CSS and JavaScript, whatever the target.
+FROM --platform=$BUILDPLATFORM node:24-alpine AS assets
 
 WORKDIR /app