diff --git a/.github/workflows/docker.yml b/.github/workflows/docker.yml
index 6fe3ca5f08..8253d3d4e8 100644
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@@ -18,6 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       TEST_TAG: zeek:latest
+      CONFFLAGS: --generator=Ninja --build-type=Release
     steps:
       - uses: actions/checkout@v2
         with:
@@ -31,7 +32,8 @@ jobs:
         with:
           context: ./
           file: docker/Dockerfile
-          # Load and tag the image so it can be used by the test job below.
+          build-args: |
+            CONFFLAGS=${{ env.CONFFLAGS }}
           load: true
           tags: ${{ env.TEST_TAG }}
 
@@ -76,6 +78,8 @@ jobs:
         with:
           context: ./
           file: docker/Dockerfile
+          build-args: |
+            CONFFLAGS=${{ env.CONFFLAGS }}
           push: true
           tags: |
             zeekurity/${{ steps.target.outputs.tag }}
diff --git a/CHANGES b/CHANGES
index 0f425b65fa..565aa3dc88 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,4 +1,14 @@
 
+4.2.0-dev.245 | 2021-10-01 14:19:19 -0700
+
+  * Enable customization of the Docker image's configure invocation (Christian Kreibich, Corelight)
+
+  * Add Python Broker module load test to Docker image btests (Christian Kreibich, Corelight)
+
+  * Set PYTHONPATH in Docker to automatically find Zeek's modules (Christian Kreibich, Corelight)
+
+  * Docker image fix: libpython needs to be 3.9 on Debian Bullseye (Christian Kreibich, Corelight)
+
 4.2.0-dev.240 | 2021-10-01 13:28:39 -0700
 
   * Bump highwayhash submodule to pull in another FreeBSD header fix (Christian Kreibich, Corelight)
diff --git a/VERSION b/VERSION
index f736e8a24d..b4b9bb78a0 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-4.2.0-dev.240
+4.2.0-dev.245
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 4ee11c65d4..5957575213 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -18,7 +18,7 @@ RUN apt-get -q update \
      libz-dev \
      make \
      python3-minimal \
-     python3-dev \
+     python3.9-dev \
      swig \
      ninja-build \
      python3-pip \
@@ -31,11 +31,10 @@ RUN apt-get -q update \
 COPY . /src/zeek
 RUN make -C /src/zeek distclean
 
+ARG CONFFLAGS="--generator=Ninja --build-type=Release"
+
 WORKDIR /src/zeek
-RUN ./configure \
-     --generator=Ninja \
-     --build-type=Release \
- && ninja -C build install
+RUN ./configure $CONFFLAGS && ninja -C build install
 
 # Final layer containing all artifacts.
 FROM debian:bullseye-slim AS final
@@ -45,7 +44,7 @@ RUN apt-get -q update \
      ca-certificates \
      git \
      libmaxminddb0 \
-     libpython3.7 \
+     libpython3.9 \
      libpcap0.8 \
      libssl1.1 \
      libz1 \
@@ -58,3 +57,4 @@ RUN apt-get -q update \
 # Copy over Zeek installation.
 COPY --from=build /usr/local/zeek /usr/local/zeek
 ENV PATH "/usr/local/zeek/bin:${PATH}"
+ENV PYTHONPATH "/usr/local/zeek/lib/zeek/python:${PYTHONPATH}"
diff --git a/docker/btest/btest.cfg b/docker/btest/btest.cfg
index 69b30b9184..bf1b17fec7 100644
--- a/docker/btest/btest.cfg
+++ b/docker/btest/btest.cfg
@@ -9,5 +9,4 @@ MinVersion  = 0.63
 [environment]
 LC_ALL=C
 PATH=%(testbase)s/../../auxil/btest:%(default_path)s
-TEST_IMAGE=${TEST_TAG:-zeek:latest}
 TZ=UTC
diff --git a/docker/btest/docker/structure_tests.sh b/docker/btest/docker/structure_tests.sh
index cb6cd2e6f0..ba20fec05a 100644
--- a/docker/btest/docker/structure_tests.sh
+++ b/docker/btest/docker/structure_tests.sh
@@ -18,3 +18,6 @@ docker run --rm "${TEST_TAG}" zkg config
 
 # Check that a plugin can be installed. We pick any plugin with minimal deps here.
 docker run --rm "${TEST_TAG}" zkg install --force sethhall/domain-tld | sed 's/(.*)/(XXX)/'
+
+# Check that the Broker Python module loads
+docker run --rm "${TEST_TAG}" python3 -c "import broker"