diff --git a/changelog.d/8390.docker b/changelog.d/8390.docker
new file mode 100644
index 0000000000..f71b8e4bbf
--- /dev/null
+++ b/changelog.d/8390.docker
@@ -0,0 +1 @@
+Add support for passing commandline args to the synapse process. Contributed by @samuel-p.
diff --git a/docker/README.md b/docker/README.md
index d0da34778e..c8f27b8566 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -83,7 +83,7 @@ docker logs synapse
 If all is well, you should now be able to connect to http://localhost:8008 and
 see a confirmation message.
 
-The following environment variables are supported in run mode:
+The following environment variables are supported in `run` mode:
 
 * `SYNAPSE_CONFIG_DIR`: where additional config files are stored. Defaults to
   `/data`.
@@ -94,6 +94,20 @@ The following environment variables are supported in run mode:
 * `UID`, `GID`: the user and group id to run Synapse as. Defaults to `991`, `991`.
 * `TZ`: the [timezone](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) the container will run with. Defaults to `UTC`.
 
+For more complex setups (e.g. for workers) you can also pass your args directly to synapse using `run` mode. For example like this:
+
+```
+docker run -d --name synapse \
+    --mount type=volume,src=synapse-data,dst=/data \
+    -p 8008:8008 \
+    matrixdotorg/synapse:latest run \
+    -m synapse.app.generic_worker \
+    --config-path=/data/homeserver.yaml \
+    --config-path=/data/generic_worker.yaml
+```
+
+If you do not provide `-m`, the value of the `SYNAPSE_WORKER` environment variable is used. If you do not provide at least one `--config-path` or `-c`, the value of the `SYNAPSE_CONFIG_PATH` environment variable is used instead.
+
 ## Generating an (admin) user
 
 After synapse is running, you may wish to create a user via `register_new_matrix_user`.
diff --git a/docker/start.py b/docker/start.py
index 9f08134158..0d2c590b88 100755
--- a/docker/start.py
+++ b/docker/start.py
@@ -179,7 +179,7 @@ def run_generate_config(environ, ownership):
 
 
 def main(args, environ):
-    mode = args[1] if len(args) > 1 else None
+    mode = args[1] if len(args) > 1 else "run"
     desired_uid = int(environ.get("UID", "991"))
     desired_gid = int(environ.get("GID", "991"))
     synapse_worker = environ.get("SYNAPSE_WORKER", "synapse.app.homeserver")
@@ -205,36 +205,47 @@ def main(args, environ):
             config_dir, config_path, environ, ownership
         )
 
-    if mode is not None:
+    if mode != "run":
         error("Unknown execution mode '%s'" % (mode,))
 
-    config_dir = environ.get("SYNAPSE_CONFIG_DIR", "/data")
-    config_path = environ.get("SYNAPSE_CONFIG_PATH", config_dir + "/homeserver.yaml")
+    args = args[2:]
 
-    if not os.path.exists(config_path):
-        if "SYNAPSE_SERVER_NAME" in environ:
-            error(
-                """\
+    if "-m" not in args:
+        args = ["-m", synapse_worker] + args
+
+    # if there are no config files passed to synapse, try adding the default file
+    if not any(p.startswith("--config-path") or p.startswith("-c") for p in args):
+        config_dir = environ.get("SYNAPSE_CONFIG_DIR", "/data")
+        config_path = environ.get(
+            "SYNAPSE_CONFIG_PATH", config_dir + "/homeserver.yaml"
+        )
+
+        if not os.path.exists(config_path):
+            if "SYNAPSE_SERVER_NAME" in environ:
+                error(
+                    """\
 Config file '%s' does not exist.
 
 The synapse docker image no longer supports generating a config file on-the-fly
 based on environment variables. You can migrate to a static config file by
 running with 'migrate_config'. See the README for more details.
 """
+                    % (config_path,)
+                )
+
+            error(
+                "Config file '%s' does not exist. You should either create a new "
+                "config file by running with the `generate` argument (and then edit "
+                "the resulting file before restarting) or specify the path to an "
+                "existing config file with the SYNAPSE_CONFIG_PATH variable."
                 % (config_path,)
             )
 
-        error(
-            "Config file '%s' does not exist. You should either create a new "
-            "config file by running with the `generate` argument (and then edit "
-            "the resulting file before restarting) or specify the path to an "
-            "existing config file with the SYNAPSE_CONFIG_PATH variable."
-            % (config_path,)
-        )
+        args += ["--config-path", config_path]
 
-    log("Starting synapse with config file " + config_path)
+    log("Starting synapse with args " + " ".join(args))
 
-    args = ["python", "-m", synapse_worker, "--config-path", config_path]
+    args = ["python"] + args
     if ownership is not None:
         args = ["gosu", ownership] + args
         os.execv("/usr/sbin/gosu", args)