diff --git a/Dockerfile b/Dockerfile
index a3b06b9..37d1157 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -16,8 +16,10 @@ WORKDIR /app
 # so it stays cached unless this block itself changes.
 # apt caches are BuildKit cache mounts: even when this layer is invalidated,
 # package downloads are reused instead of hitting deb.debian.org again.
+# deb.debian.org is slow from CN networks, so point apt at a local mirror first.
 RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     --mount=type=cache,target=/var/lib/apt,sharing=locked \
+    sed -i 's|deb\.debian\.org|mirrors.aliyun.com|g' /etc/apt/sources.list.d/debian.sources && \
     apt-get update && \
     apt-get install -y --no-install-recommends ffmpeg aria2 curl tini gosu ca-certificates unzip \
         chromium libnss3 libfreetype6 libharfbuzz0b fonts-freefont-ttf && \