diff --git a/Dockerfile.standalone b/Dockerfile.standalone
index 0c2d703..1152b9e 100644
--- a/Dockerfile.standalone
+++ b/Dockerfile.standalone
@@ -3,7 +3,7 @@
 #   1. Local: place files in prebuilt/qemu/ (from build-qemu.sh or manual copy)
 #   2. CI/CD: downloads from GitHub Release (requires qemu-lcgamboa repo to be public)
 # The COPY always runs; the RUN only downloads missing files.
-FROM ubuntu:20.04 AS qemu-provider
+FROM debian:bookworm-slim AS qemu-provider
 
 RUN apt-get update && apt-get install -y --no-install-recommends curl ca-certificates \
     && rm -rf /var/lib/apt/lists/*
@@ -28,7 +28,7 @@ RUN cd /qemu \
 
 
 # ---- Stage 0.5: ESP-IDF toolchain for ESP32 compilation ----
-FROM ubuntu:20.04 AS espidf-builder
+FROM debian:bookworm-slim AS espidf-builder
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     git wget flex bison gperf python3 python3-pip python3-venv \