diff --git a/docker/python-builder/scripts/assemble b/docker/python-builder/scripts/assemble
index 3d0131605b..83a9ba939d 100755
--- a/docker/python-builder/scripts/assemble
+++ b/docker/python-builder/scripts/assemble
@@ -27,53 +27,66 @@ cd /tmp/src
 
 apt-get update
 
-# Protect from the bindep builder image use of the assemble script
-# to produce a wheel
-if [ -f bindep.txt -o -f other-requirements.txt ] ; then
-  bindep -l newline > /output/bindep/run.txt || true
-  compile_packages=$(bindep -b compile || true)
-  if [ ! -z "$compile_packages" ] ; then
-    apt-get install -y ${compile_packages}
-  fi
-fi
-
 # pbr needs git installed, else nothing will work
 apt-get install -y git
 
-# Build a wheel so that we have an install target.
-# pip install . in the container context with the mounted
-# source dir gets ... exciting.
-# We run sdist first to trigger code generation steps such
-# as are found in zuul, since the sequencing otherwise
-# happens in a way that makes wheel content copying unhappy.
-# pip wheel isn't used here because it puts all of the output
-# in the output dir and not the wheel cache, so it's not
-# possible to tell what is the wheel for the project and
-# what is the wheel cache.
-python setup.py sdist bdist_wheel -d /output/wheels
-
-# Use a virtualenv for the next install steps in case to prevent
-# things from the current environment from making us not build a
-# wheel.
+# Use a clean virtualenv for install steps to prevent things from the
+# current environment making us not build a wheel.
 python -m venv /tmp/venv
 /tmp/venv/bin/pip install -U pip wheel
 
-# Install everything so that the wheel cache is populated
-# with transitive depends. If a requirements.txt file exists,
-# install it directly so that people can use git url syntax
-# to do things like pick up patched but unreleased versions
-# of dependencies.
-if [ -f /tmp/src/requirements.txt ] ; then
-    /tmp/venv/bin/pip install --cache-dir=/output/wheels -r /tmp/src/requirements.txt
-    cp /tmp/src/requirements.txt /output/requirements.txt
-fi
-/tmp/venv/bin/pip install --cache-dir=/output/wheels /output/wheels/*whl
+function install_pwd {
+    # Protect from the bindep builder image use of the assemble script
+    # to produce a wheel.  Note we append because we want all
+    # sibling packages in here too
+    if [ -f bindep.txt -o -f other-requirements.txt ] ; then
+        bindep -l newline >> /output/bindep/run.txt || true
+        compile_packages=$(bindep -b compile || true)
+        if [ ! -z "$compile_packages" ] ; then
+            apt-get install -y ${compile_packages}
+        fi
+    fi
 
-# Install each of the extras so that we collect all possibly
-# needed wheels in the wheel cache. get-extras-packages also
-# writes out the req files into /output/$extra/requirements.txt.
-for req in $(get-extras-packages) ; do
-    /tmp/venv/bin/pip install --cache-dir=/output/wheels "$req"
+    # Build a wheel so that we have an install target.
+    # pip install . in the container context with the mounted
+    # source dir gets ... exciting.
+    # We run sdist first to trigger code generation steps such
+    # as are found in zuul, since the sequencing otherwise
+    # happens in a way that makes wheel content copying unhappy.
+    # pip wheel isn't used here because it puts all of the output
+    # in the output dir and not the wheel cache, so it's not
+    # possible to tell what is the wheel for the project and
+    # what is the wheel cache.
+    python setup.py sdist bdist_wheel -d /output/wheels
+
+    # Install everything so that the wheel cache is populated with
+    # transitive depends. If a requirements.txt file exists, install
+    # it directly so that people can use git url syntax to do things
+    # like pick up patched but unreleased versions of dependencies.
+    # Only do this for the main package (i.e. only write requirements
+    # once).
+    if [ -f /tmp/src/requirements.txt ] && [ ! -f /output/requirements.txt ] ; then
+        /tmp/venv/bin/pip install --cache-dir=/output/wheels -r /tmp/src/requirements.txt
+        cp /tmp/src/requirements.txt /output/requirements.txt
+    fi
+    /tmp/venv/bin/pip install --cache-dir=/output/wheels /output/wheels/*whl
+
+    # Install each of the extras so that we collect all possibly
+    # needed wheels in the wheel cache. get-extras-packages also
+    # writes out the req files into /output/$extra/requirements.txt.
+    for req in $(get-extras-packages) ; do
+        /tmp/venv/bin/pip install --cache-dir=/output/wheels "$req"
+    done
+}
+
+# Install the main package
+install_pwd
+
+# go through ZUUL_SIBLINGS, if any, and build those wheels too
+for sibling in ${ZUUL_SIBLINGS:-}; do
+    pushd .zuul-siblings/${sibling}
+    install_pwd
+    popd
 done
 
 rm -rf /tmp/venv
diff --git a/docker/python-builder/scripts/install-from-bindep b/docker/python-builder/scripts/install-from-bindep
index 4733ac9e31..b78343bc6e 100755
--- a/docker/python-builder/scripts/install-from-bindep
+++ b/docker/python-builder/scripts/install-from-bindep
@@ -25,7 +25,12 @@ apt-get -y install $(cat /output/bindep/run.txt)
 if [ -f /output/requirements.txt ] ; then
     pip install --cache-dir=/output/wheels -r /output/requirements.txt
 fi
-pip install --cache-dir=/output/wheels /output/wheels/*.whl
+
+# Install the wheels.  Use --force here because sibling wheels might
+# be built with the same version number as the latest release, but we
+# really want the speculatively built wheels installed over any
+# automatic dependencies.
+pip install --force --cache-dir=/output/wheels /output/wheels/*.whl
 
 # clean up after ourselves
 apt-get clean