diff --git a/deploy/docker/Dockerfile.shoresh_engine b/deploy/docker/Dockerfile.shoresh_engine
index bd636b15..96430511 100644
--- a/deploy/docker/Dockerfile.shoresh_engine
+++ b/deploy/docker/Dockerfile.shoresh_engine
@@ -5,7 +5,11 @@
 # === BUILD STAGE ===
 FROM haskell:9.6.4-slim AS build
 
-RUN apt-get update && apt-get install -y zlib1g-dev && rm -rf /var/lib/apt/lists/*
+# haskell:9.6.4-slim is Debian Buster (EOL) — use archive repos
+RUN sed -i 's|deb.debian.org/debian|archive.debian.org/debian|g' /etc/apt/sources.list && \
+    sed -i 's|deb.debian.org/debian-security|archive.debian.org/debian-security|g' /etc/apt/sources.list && \
+    sed -i '/buster-updates/d' /etc/apt/sources.list && \
+    apt-get update && apt-get install -y zlib1g-dev && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app