diff --git a/debian/build_virtualenv b/debian/build_virtualenv
index e691163619..71d50a43ce 100755
--- a/debian/build_virtualenv
+++ b/debian/build_virtualenv
@@ -43,7 +43,8 @@ dh_virtualenv \
     --preinstall="wheel" \
     --extra-pip-arg="--no-cache-dir" \
     --extra-pip-arg="--compile" \
-    --extras="all,systemd,test"
+    --extras="all,systemd,test" \
+    --requirements="requirements.txt"
 
 PACKAGE_BUILD_DIR="debian/matrix-synapse-py3"
 VIRTUALENV_DIR="${PACKAGE_BUILD_DIR}${DH_VIRTUALENV_INSTALL_ROOT}/matrix-synapse"
diff --git a/docker/Dockerfile-dhvirtualenv b/docker/Dockerfile-dhvirtualenv
index fbc1d2346f..0922e9d526 100644
--- a/docker/Dockerfile-dhvirtualenv
+++ b/docker/Dockerfile-dhvirtualenv
@@ -85,6 +85,15 @@ RUN apt-get update -qq -o Acquire::Languages=none \
         libpq-dev \
         xmlsec1
 
+RUN pip3 install -U \
+    pip \
+    setuptools \
+    wheel
+
+# We normally use poetry 1.1.12. However we need to use a prerelease of 1.2 here,
+# which fixes a bug in poetry export that stops us from exporting for Python 3.8 builds.
+RUN pip3 install poetry==1.2.0b1
+
 COPY --from=builder /dh-virtualenv_1.2.2-1_all.deb /
 
 # install dhvirtualenv. Update the apt cache again first, in case we got a
diff --git a/docker/build_debian.sh b/docker/build_debian.sh
index 9eae38af91..5adfbb48ca 100644
--- a/docker/build_debian.sh
+++ b/docker/build_debian.sh
@@ -11,6 +11,9 @@ DIST=$(cut -d ':' -f2 <<< "${distro:?}")
 cp -aT /synapse/source /synapse/build
 cd /synapse/build
 
+# Export a requirements.txt file for the dh-virtualenv to use
+poetry export --extras "all test" -o requirements.txt
+
 # if this is a prerelease, set the Section accordingly.
 #
 # When the package is later added to the package repo, reprepro will use the