diff --git a/synapse/rest/client/v1/register.py b/synapse/rest/client/v1/register.py
index ef56d1e90f..a923d5a198 100644
--- a/synapse/rest/client/v1/register.py
+++ b/synapse/rest/client/v1/register.py
@@ -410,7 +410,7 @@ class CreateUserRestServlet(ClientV1RestServlet):
             raise SynapseError(400, "Failed to parse 'duration_seconds'")
         if duration_seconds > self.direct_user_creation_max_duration:
             duration_seconds = self.direct_user_creation_max_duration
-        password_hash = user_json["password_hash"].encode("utf-8") if user_json["password_hash"] else None
+        password_hash = user_json["password_hash"].encode("utf-8") if user_json.get("password_hash") else None
 
         handler = self.handlers.registration_handler
         user_id, token = yield handler.get_or_create_user(