diff --git a/roles/matrix-postgres/tasks/import_synapse_sqlite_db.yml b/roles/matrix-postgres/tasks/import_synapse_sqlite_db.yml
index a459b6e1..b885ea97 100644
--- a/roles/matrix-postgres/tasks/import_synapse_sqlite_db.yml
+++ b/roles/matrix-postgres/tasks/import_synapse_sqlite_db.yml
@@ -83,7 +83,7 @@
       --mount type=bind,src={{ matrix_synapse_config_dir_path }},dst=/data
       --mount type=bind,src={{ matrix_synapse_config_dir_path }},dst=/matrix-media-store-parent/media-store
       --mount type=bind,src={{ server_path_homeserver_db }},dst=/{{ server_path_homeserver_db | basename }}
-      {{ matrix_synapse_docker_image }}
+      {{ matrix_synapse_docker_image_final }}
       /usr/local/bin/synapse_port_db --sqlite-database /{{ server_path_homeserver_db | basename }} --postgres-config /data/homeserver.yaml
   register: matrix_postgres_import_synapse_sqlite_db_result
   changed_when: matrix_postgres_import_synapse_sqlite_db_result.rc == 0
diff --git a/roles/matrix-synapse/defaults/main.yml b/roles/matrix-synapse/defaults/main.yml
index d117eaaf..40e05be7 100644
--- a/roles/matrix-synapse/defaults/main.yml
+++ b/roles/matrix-synapse/defaults/main.yml
@@ -7,14 +7,47 @@ matrix_synapse_enabled: true
 matrix_synapse_container_image_self_build: false
 matrix_synapse_container_image_self_build_repo: "https://github.com/matrix-org/synapse.git"
 
+# matrix_synapse_container_image_customizations_enabled controls whether a customized Synapse image will be built.
+#
+# We toggle this variable to `true` when certain features which require a custom build are enabled.
+# Feel free to toggle this to `true` yourself and specify build steps in `matrix_synapse_container_image_customizations_dockerfile_body_custom`.
+#
+# See:
+# - `roles/matrix-synapse/templates/synapse/customizations/Dockerfile.j2`
+# - `matrix_synapse_container_image_customizations_dockerfile_body_custom`
+# - `matrix_synapse_docker_image_customized`
+# - `matrix_synapse_docker_image_final`
+matrix_synapse_container_image_customizations_enabled: "{{ matrix_synapse_ext_synapse_s3_storage_provider_enabled }}"
+
+# matrix_synapse_container_image_customizations_dockerfile_body contains your custom Dockerfile steps
+# for building your customized Synapse image based on the original (upstream) image (`matrix_synapse_docker_image`).
+# A `FROM ...` clause is included automatically so you don't have to.
+#
+# Example:
+# matrix_synapse_container_image_customizations_dockerfile_body_custom: |
+#  RUN echo 'This is a custom step for building the customized Docker image for Synapse.'
+#  RUN echo 'You can override matrix_synapse_container_image_customizations_dockerfile_body_custom to add your own steps.'
+#  RUN echo 'Note that matrix_synapse_container_image_customizations_dockerfile_body_auto injects steps before this.'
+#  RUN echo 'You do NOT need to include a FROM clause yourself.'
+matrix_synapse_container_image_customizations_dockerfile_body_custom: ''
+
 matrix_synapse_docker_image: "{{ matrix_synapse_docker_image_name_prefix }}matrixdotorg/synapse:{{ matrix_synapse_docker_image_tag }}"
 matrix_synapse_docker_image_name_prefix: "{{ 'localhost/' if matrix_synapse_container_image_self_build else matrix_container_global_registry_prefix }}"
 matrix_synapse_version: v1.68.0
 matrix_synapse_docker_image_tag: "{{ matrix_synapse_version }}"
 matrix_synapse_docker_image_force_pull: "{{ matrix_synapse_docker_image.endswith(':latest') }}"
 
+# matrix_synapse_docker_image_customized is the name of the locally built Synapse image
+# which adds various customizations on top of the original (upstream) Synapse image.
+# This image will be based on the upstream `matrix_synapse_docker_image` image, only if `matrix_synapse_container_image_customizations_enabled: true`.
+matrix_synapse_docker_image_customized: "localhost/matrixdotorg/synapse:{{ matrix_synapse_docker_image_tag }}-customized"
+
+# matrix_synapse_docker_image_final holds the name of the Synapse image to run depending on whether or not customizations are enabled.
+matrix_synapse_docker_image_final: "{{ matrix_synapse_docker_image_customized if matrix_synapse_container_image_customizations_enabled else matrix_synapse_docker_image }} "
+
 matrix_synapse_base_path: "{{ matrix_base_data_path }}/synapse"
 matrix_synapse_docker_src_files_path: "{{ matrix_synapse_base_path }}/docker-src"
+matrix_synapse_customized_docker_src_files_path: "{{ matrix_synapse_base_path }}/customized-docker-src"
 matrix_synapse_config_dir_path: "{{ matrix_synapse_base_path }}/config"
 matrix_synapse_storage_path: "{{ matrix_synapse_base_path }}/storage"
 matrix_synapse_media_store_path: "{{ matrix_synapse_storage_path }}/media-store"
diff --git a/roles/matrix-synapse/tasks/setup_synapse.yml b/roles/matrix-synapse/tasks/setup_synapse.yml
index d4e6ae95..7b887f30 100644
--- a/roles/matrix-synapse/tasks/setup_synapse.yml
+++ b/roles/matrix-synapse/tasks/setup_synapse.yml
@@ -11,6 +11,7 @@
     - {path: "{{ matrix_synapse_config_dir_path }}", when: true}
     - {path: "{{ matrix_synapse_ext_path }}", when: true}
     - {path: "{{ matrix_synapse_docker_src_files_path }}", when: "{{ matrix_synapse_container_image_self_build }}"}
+    - {path: "{{ matrix_synapse_customized_docker_src_files_path }}", when: "{{ matrix_synapse_container_image_customizations_enabled }}"}
     # We handle matrix_synapse_media_store_path elsewhere (in ./synapse/setup_install.yml),
     # because if it's using Goofys and it's already mounted (from before),
     # trying to chown/chmod it here will cause trouble.
diff --git a/roles/matrix-synapse/tasks/synapse/setup_install.yml b/roles/matrix-synapse/tasks/synapse/setup_install.yml
index aea03f05..4d0e749f 100644
--- a/roles/matrix-synapse/tasks/synapse/setup_install.yml
+++ b/roles/matrix-synapse/tasks/synapse/setup_install.yml
@@ -62,6 +62,25 @@
   delay: "{{ matrix_container_retries_delay }}"
   until: result is not failed
 
+- when: "matrix_synapse_container_image_customizations_enabled | bool"
+  block:
+    - name: Ensure customizations Dockerfile is created
+      ansible.builtin.template:
+        src: "{{ role_path }}/templates/synapse/customizations/Dockerfile.j2"
+        dest: "{{ matrix_synapse_customized_docker_src_files_path }}/Dockerfile"
+        owner: "{{ matrix_user_username }}"
+        group: "{{ matrix_user_groupname }}"
+        mode: 0640
+
+    - name: Ensure customized Docker image for Synapse is built
+      docker_image:
+        name: "{{ matrix_synapse_docker_image_customized }}"
+        source: build
+        build:
+          dockerfile: Dockerfile
+          path: "{{ matrix_synapse_customized_docker_src_files_path }}"
+          pull: true
+
 - name: Check if a Synapse signing key exists
   ansible.builtin.stat:
     path: "{{ matrix_synapse_config_dir_path }}/{{ matrix_server_fqn_matrix }}.signing.key"
diff --git a/roles/matrix-synapse/tasks/synapse/setup_uninstall.yml b/roles/matrix-synapse/tasks/synapse/setup_uninstall.yml
index 17b1b8c4..06e55014 100644
--- a/roles/matrix-synapse/tasks/synapse/setup_uninstall.yml
+++ b/roles/matrix-synapse/tasks/synapse/setup_uninstall.yml
@@ -27,8 +27,11 @@
 
 - name: Ensure Synapse Docker image doesn't exist
   docker_image:
-    name: "{{ matrix_synapse_docker_image }}"
+    name: "{{ item }}"
     state: absent
+  with_items:
+    - "{{ matrix_synapse_docker_image_final }}"
+    - "{{ matrix_synapse_docker_image }}"
 
 - name: Ensure sample prometheus.yml for external scraping is deleted
   ansible.builtin.file:
diff --git a/roles/matrix-synapse/templates/synapse/customizations/Dockerfile.j2 b/roles/matrix-synapse/templates/synapse/customizations/Dockerfile.j2
new file mode 100644
index 00000000..7cce2086
--- /dev/null
+++ b/roles/matrix-synapse/templates/synapse/customizations/Dockerfile.j2
@@ -0,0 +1,3 @@
+FROM {{ matrix_synapse_docker_image }}
+
+{{ matrix_synapse_container_image_customizations_dockerfile_body_custom }}
diff --git a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2 b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2
index 96b65a0a..3855b850 100644
--- a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2
+++ b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2
@@ -42,7 +42,7 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name {{ matrix_synapse_wor
 			{% for arg in matrix_synapse_container_arguments %}
 			{{ arg }} \
 			{% endfor %}
-			{{ matrix_synapse_docker_image }} \
+			{{ matrix_synapse_docker_image_final }} \
 			run -m synapse.app.{{ matrix_synapse_worker_details.app }} -c /data/homeserver.yaml -c /data/{{ matrix_synapse_worker_config_file_name }}
 
 
diff --git a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2 b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2
index eed50ad1..f41cc54c 100644
--- a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2
+++ b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2
@@ -60,7 +60,7 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-synapse \
 			{% for arg in matrix_synapse_container_arguments %}
 			{{ arg }} \
 			{% endfor %}
-			{{ matrix_synapse_docker_image }} \
+			{{ matrix_synapse_docker_image_final }} \
 			run -m synapse.app.homeserver -c /data/homeserver.yaml
 
 ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-synapse 2>/dev/null || true'