diff --git a/contrib/docker/start.py b/contrib/docker/start.py
index 2c427ba1b7..e50d23be5f 100755
--- a/contrib/docker/start.py
+++ b/contrib/docker/start.py
@@ -3,7 +3,7 @@
 import jinja2
 import os
 import sys
-import socket
+import subprocess
 
 convert = lambda src, dst: open(dst, "w").write(jinja2.Template(open(src).read()).render(**os.environ))
 mode = sys.argv[1] if len(sys.argv) > 1 else None
@@ -12,19 +12,20 @@ if "SYNAPSE_SERVER_NAME" not in os.environ:
     print("Environment variable SYNAPSE_SERVER_NAME is mandatory, exiting.")
     sys.exit(2)
 
-params = ["--server-name", os.environ.get("SYNAPSE_SERVER_NAME"),
-          "--report-stats", os.environ.get("SYNAPSE_REPORT_STATS", "no"),
-          "--config-path", os.environ.get("SYNAPSE_CONFIG_PATH", "/compiled/homeserver.yaml")]
-
-if mode == "generate":
-    params.append("--generate-config")
+args = ["python", "-m", "synapse.app.homeserver",
+        "--server-name", os.environ.get("SYNAPSE_SERVER_NAME"),
+        "--report-stats", os.environ.get("SYNAPSE_REPORT_STATS", "no"),
+        "--config-path", os.environ.get("SYNAPSE_CONFIG_PATH", "/compiled/homeserver.yaml")]
 
 # Parse the configuration file
-if not os.path.exists("/compiled"):
-    os.mkdir("/compiled")
-
+if not os.path.exists("/compiled"): os.mkdir("/compiled")
 convert("/conf/homeserver.yaml", "/compiled/homeserver.yaml")
 convert("/conf/log.config", "/compiled/%s.log.config" % os.environ.get("SYNAPSE_SERVER_NAME"))
 
-# TODO, replace with a call to synapse.app.homeserver.run()
-os.execv("/usr/local/bin/python", ["python", "-m", "synapse.app.homeserver"] + params)
+# In generate mode, generate a configuration, missing keys, then exit
+if mode == "generate":
+    os.execv("/usr/local/bin/python", args + ["--generate-config"])
+# In normal mode, generate missing keys if any, then run synapse
+else:
+    subprocess.check_output(args + ["--generate-keys"])
+    os.execv("/usr/local/bin/python", args)