diff --git a/.github/workflows/docker-publish.yml b/.github/workflows/docker-publish.yml
index 27be0670..8713f5f3 100644
--- a/.github/workflows/docker-publish.yml
+++ b/.github/workflows/docker-publish.yml
@@ -17,6 +17,8 @@ on:
 jobs:
   docker:
     runs-on: ubuntu-latest
+    # A healthy build takes a few minutes; fail fast instead of hanging for 6 hours.
+    timeout-minutes: 30
     permissions:
       contents: read
       packages: write
diff --git a/Dockerfile b/Dockerfile
index 18669254..81d1ceb2 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,7 @@
-FROM docker.io/library/node:24.16.0-alpine3.22 AS mermaid-live-editor-dependencies
+# The build output is a static site, so build it once on the runner's native
+# platform instead of under QEMU emulation; only the nginx stage below is
+# per-architecture.
+FROM --platform=$BUILDPLATFORM docker.io/library/node:24.16.0-alpine3.22 AS mermaid-live-editor-dependencies
 
 RUN apk --no-cache add build-base git python3 && \
     rm -rf /var/cache/apk/*