diff --git a/Dockerfile b/Dockerfile
index ec36562..89bf44b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,8 @@
 # ruby:3.1-bullseye, pinned 2026-02-22
-FROM ruby@sha256:4cc0e5aaa726f8c2cbf1dfc8e5ecd459dbfbebe44b5eee5da6f79ffcc1b6c36f AS builder
+# (ruby:3.1-buster is EOL; bullseye is the supported equivalent)
+FROM ruby@sha256:077cdae43603fc568f4c65a2558cb608299b84c93e88c0048e6f3bdf3fa138fd AS builder
 
-RUN apt-get update && apt-get install -y --no-install-recommends \
+RUN apt update && apt install -y \
     bsdmainutils \
     build-essential \
     make \
@@ -12,8 +13,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libxslt-dev \
     pkg-config \
     python3 \
-    xz-utils \
-    && rm -rf /var/lib/apt/lists/*
+    xz-utils
 
 # Node.js 20.18.3 LTS, pinned by sha256
 RUN cd /tmp && \