diff --git a/.github/workflows/build_python_runtime.yml b/.github/workflows/build_python_runtime.yml
index d47fefcaa..8b29a41e8 100644
--- a/.github/workflows/build_python_runtime.yml
+++ b/.github/workflows/build_python_runtime.yml
@@ -26,7 +26,7 @@ env:
 # Unfortunately these jobs cannot be easily written as a matrix since `matrix.exclude` does not
 # support expression syntax, and the `inputs` context is not available inside the job `if` key.
 jobs:
-  build-and-upload-heroku-20:
+  heroku-20:
     runs-on: pub-hk-ubuntu-22.04-xlarge
     env:
       STACK_VERSION: "20"
@@ -34,15 +34,15 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Build Docker image
-        run: docker build --pull --tag buildenv --build-arg=STACK_VERSION builds/
+        run: docker build --platform="linux/amd64" --pull --tag buildenv --build-arg=STACK_VERSION builds/
       - name: Build and package Python runtime
-        run: docker run --rm --platform="linux/amd64" --volume="${PWD}/upload:/tmp/upload" buildenv ./build_python_runtime.sh "${{ inputs.python_version }}"
+        run: docker run --rm --volume="${PWD}/upload:/tmp/upload" buildenv ./build_python_runtime.sh "${{ inputs.python_version }}"
       - name: Upload Python runtime archive to S3
         if: (!inputs.dry_run)
         run: aws s3 sync ./upload "s3://${S3_BUCKET}"
 
-  build-and-upload-heroku-22:
-    # We only support Python 3.9+ on Heroku-22.
+  heroku-22:
+    # On Heroku-22 we only support Python 3.9+.
     if: (!startsWith(inputs.python_version,'3.8.'))
     runs-on: pub-hk-ubuntu-22.04-xlarge
     env:
@@ -51,9 +51,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Build Docker image
-        run: docker build --pull --tag buildenv --build-arg=STACK_VERSION builds/
+        run: docker build --platform="linux/amd64" --pull --tag buildenv --build-arg=STACK_VERSION builds/
       - name: Build and package Python runtime
-        run: docker run --rm --platform="linux/amd64" --volume="${PWD}/upload:/tmp/upload" buildenv ./build_python_runtime.sh "${{ inputs.python_version }}"
+        run: docker run --rm --volume="${PWD}/upload:/tmp/upload" buildenv ./build_python_runtime.sh "${{ inputs.python_version }}"
       - name: Upload Python runtime archive to S3
         if: (!inputs.dry_run)
         run: aws s3 sync ./upload "s3://${S3_BUCKET}"
diff --git a/builds/Dockerfile b/builds/Dockerfile
index 37e25c26f..84672acb0 100644
--- a/builds/Dockerfile
+++ b/builds/Dockerfile
@@ -1,11 +1,11 @@
 ARG STACK_VERSION="22"
-FROM --platform=linux/amd64 heroku/heroku:${STACK_VERSION}-build
+FROM heroku/heroku:${STACK_VERSION}-build
 
 ARG STACK_VERSION
 ENV STACK="heroku-${STACK_VERSION}"
 
-RUN apt-get update \
-    && apt-get install --no-install-recommends -y \
+RUN apt-get update --error-on=any \
+    && apt-get install -y --no-install-recommends \
       libsqlite3-dev \
     && rm -rf /var/lib/apt/lists/*
 
diff --git a/builds/build_python_runtime.sh b/builds/build_python_runtime.sh
index 379505e63..4735039f0 100755
--- a/builds/build_python_runtime.sh
+++ b/builds/build_python_runtime.sh
@@ -7,7 +7,7 @@ PYTHON_MAJOR_VERSION="${PYTHON_VERSION%.*}"
 
 INSTALL_DIR="/app/.heroku/python"
 SRC_DIR="/tmp/src"
-ARCHIVES_DIR="/tmp/upload/${STACK}/runtimes"
+UPLOAD_DIR="/tmp/upload/${STACK}/runtimes"
 
 function error() {
   echo "Error: ${1}" >&2
@@ -67,7 +67,7 @@ SIGNATURE_URL="${SOURCE_URL}.asc"
 
 set -o xtrace
 
-mkdir -p "${SRC_DIR}" "${INSTALL_DIR}" "${ARCHIVES_DIR}"
+mkdir -p "${SRC_DIR}" "${INSTALL_DIR}" "${UPLOAD_DIR}"
 
 curl --fail --retry 3 --retry-connrefused --connect-timeout 10 --max-time 60 -o python.tgz "${SOURCE_URL}"
 curl --fail --retry 3 --retry-connrefused --connect-timeout 10 --max-time 60 -o python.tgz.asc "${SIGNATURE_URL}"
@@ -191,13 +191,12 @@ LD_LIBRARY_PATH="${SRC_DIR}" "${SRC_DIR}/python" -m compileall -f --invalidation
 # This symlink must be relative, to ensure that the Python install remains relocatable.
 ln -srvT "${INSTALL_DIR}/bin/python3" "${INSTALL_DIR}/bin/python"
 
-cd "${ARCHIVES_DIR}"
-
 # The tar file is gzipped separately, so we can set a higher gzip compression level than
 # the default. In the future we'll also want to create a second archive that used zstd.
-TAR_FILENAME="python-${PYTHON_VERSION}.tar"
-tar --create --format=pax --sort=name --verbose --file "${TAR_FILENAME}" --directory="${INSTALL_DIR}" .
-gzip --best "${TAR_FILENAME}"
+# Results in a compressed archive filename of form: 'python-X.Y.Z.tar.gz'
+TAR_FILEPATH="${UPLOAD_DIR}/python-${PYTHON_VERSION}.tar"
+tar --create --format=pax --sort=name --file "${TAR_FILEPATH}" --directory="${INSTALL_DIR}" .
+gzip --best "${TAR_FILEPATH}"
 
 du --max-depth 1 --human-readable "${INSTALL_DIR}"
-du --all --human-readable "${ARCHIVES_DIR}"
+du --all --human-readable "${UPLOAD_DIR}"