diff --git a/roles/build-container-image/common.rst b/roles/build-container-image/common.rst
index 3bbfedaaa..b9a3d0eba 100644
--- a/roles/build-container-image/common.rst
+++ b/roles/build-container-image/common.rst
@@ -133,10 +133,15 @@ role to install Docker or Podman before using these roles.
 
       A list of tags to be added to the image when promoted.
 
-   .. zuul:rolevar:: tags
+   .. zuul:rolevar:: siblings
       :type: list
-      :default: ['latest']
+      :default: []
 
-      A list of tags to be added to the image when promoted.
+      A list of sibling projects to be copied into
+      ``{{zuul_work_dir}}/.zuul-siblings``.  This can be useful to
+      collect multiple projects to be installed within the same Docker
+      context.  A ``-build-arg`` called ``ZUUL_SIBLINGS`` will be
+      added with each sibling project.  Note that projects here must
+      be listed in ``required-projects``.
 
 .. _anchors: https://yaml.org/spec/1.2/spec.html#&%20anchor//
diff --git a/roles/build-container-image/tasks/build.yaml b/roles/build-container-image/tasks/build.yaml
new file mode 100644
index 000000000..b5e5d0bf1
--- /dev/null
+++ b/roles/build-container-image/tasks/build.yaml
@@ -0,0 +1,50 @@
+- name: Check sibling directory
+  stat:
+    path: '{{ zuul_work_dir }}/{{ item.context }}/.zuul-siblings'
+  register: _dot_zuul_siblings
+
+# This should have been cleaned up; multiple builds may specify
+# different siblings to include so we need to start fresh.
+- name: Check for clean build
+  assert:
+    that: not _dot_zuul_siblings.stat.exists
+
+- name: Create sibling source directory
+  file:
+    path: '{{ zuul_work_dir }}/{{ item.context }}/.zuul-siblings'
+    state: directory
+    mode: 0755
+  when: item.siblings is defined
+
+- name: Copy sibling source directories
+  command:
+    cmd: 'cp --parents -r {{ sibling }} /home/zuul/{{ zuul_work_dir }}/{{ item.context }}/.zuul-siblings'
+    chdir: '~/src'
+  loop: '{{ item.siblings }}'
+  loop_control:
+    loop_var: sibling
+  when: item.siblings is defined
+
+- name: Build a container image
+  command: >-
+    {{ container_command }} build {{ item.path | default('.') }} {% if containerfile %}-f {{ containerfile }}{% endif %}
+    {% if item.target | default(false) -%}
+      --target {{ item.target }}
+    {% endif -%}
+    {% for build_arg in item.build_args | default([]) -%}
+      --build-arg {{ build_arg }}
+    {% endfor -%}
+    {% if items.siblings | default(false) -%}
+      --build-arg "ZUUL_SIBLINGS={{ item.siblings | join(' ') }}"
+    {% endif -%}
+    {% for tag in item.tags | default(['latest']) -%}
+    --tag {{ item.repository }}:change_{{ zuul.change }}_{{ tag }}
+    --tag {{ item.repository }}:{{ tag }}
+    {% endfor -%}
+  args:
+    chdir: "{{ zuul_work_dir }}/{{ item.context }}"
+
+- name: Cleanup sibling source directory
+  file:
+    path: '{{ zuul_work_dir }}/.zuul-siblings'
+    state: absent
diff --git a/roles/build-container-image/tasks/main.yaml b/roles/build-container-image/tasks/main.yaml
index c9296c447..42dfd716a 100644
--- a/roles/build-container-image/tasks/main.yaml
+++ b/roles/build-container-image/tasks/main.yaml
@@ -4,25 +4,15 @@
   set_fact:
     buildset_registry: "{{ (lookup('file', zuul.executor.work_root + '/results.json') | from_json)['buildset_registry'] }}"
   ignore_errors: true
+
 - name: Set container filename arg
   set_fact:
     containerfile: "{{ item.container_filename|default(container_filename|default('')) }}"
-- name: Build a container image
-  command: >-
-    {{ container_command }} build {{ item.path | default('.') }} {% if containerfile %}-f {{ containerfile }}{% endif %}
-    {% if item.target | default(false) -%}
-      --target {{ item.target }}
-    {% endif -%}
-    {% for build_arg in item.build_args | default([]) -%}
-      --build-arg {{ build_arg }}
-    {% endfor -%}
-    {% for tag in item.tags | default(['latest']) -%}
-    --tag {{ item.repository }}:change_{{ zuul.change }}_{{ tag }}
-    --tag {{ item.repository }}:{{ tag }}
-    {% endfor -%}
-  args:
-    chdir: "{{ zuul_work_dir }}/{{ item.context }}"
+
+- name: Build container images
+  include_tasks: build.yaml
   loop: "{{ container_images }}"
+
 # Docker, and therefore skopeo and podman, don't understand docker
 # push [1234:5678::]:5000/image/path:tag so we set up /etc/hosts with
 # a registry alias name to support ipv6 and 4.