diff --git a/changelog.d/20156.misc b/changelog.d/20156.misc
new file mode 100644
index 0000000000..116a238d8f
--- /dev/null
+++ b/changelog.d/20156.misc
@@ -0,0 +1 @@
+[MSC4140: Cancellable delayed events](https://github.com/matrix-org/matrix-spec-proposals/pull/4140): Update the error response for requesting to schedule a delayed event with a delay that exceeds the server-enforced maximum delay.
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index 0c2b41225a..78fd8c3a60 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -137,6 +137,8 @@ class Codes(str, Enum):
     PROFILE_TOO_LARGE = "M_PROFILE_TOO_LARGE"
     KEY_TOO_LARGE = "M_KEY_TOO_LARGE"
 
+    DELAY_TOO_LARGE = "ORG.MATRIX.MSC4140_DELAY_TOO_LARGE"
+
     # Part of MSC4155/MSC4380
     INVITE_BLOCKED = "M_INVITE_BLOCKED"
 
diff --git a/synapse/handlers/delayed_events.py b/synapse/handlers/delayed_events.py
index cfaf16a30c..ac2da15112 100644
--- a/synapse/handlers/delayed_events.py
+++ b/synapse/handlers/delayed_events.py
@@ -373,9 +373,9 @@ class DelayedEventsHandler:
             requested_delay = delay.as_millis()
             max_delay = self._config.server.max_event_delay_duration.as_millis()
             raise SynapseError(
-                HTTPStatus.FORBIDDEN,
+                HTTPStatus.BAD_REQUEST,
                 f"The requested delay ({requested_delay}ms) exceeds the allowed maximum ({max_delay}ms)",
-                Codes.FORBIDDEN,
+                Codes.DELAY_TOO_LARGE,
             )
 
         self._event_creation_handler.validator.validate_builder(
diff --git a/tests/rest/client/test_rooms.py b/tests/rest/client/test_rooms.py
index a6f5043c92..78c960a537 100644
--- a/tests/rest/client/test_rooms.py
+++ b/tests/rest/client/test_rooms.py
@@ -2567,9 +2567,9 @@ class RoomDelayedEventTestCase(RoomBase):
             ).encode("ascii"),
             {"body": "test", "msgtype": "m.text"},
         )
-        self.assertEqual(HTTPStatus.FORBIDDEN, channel.code, channel.result)
+        self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, channel.result)
         self.assertEqual(
-            Codes.FORBIDDEN,
+            "ORG.MATRIX.MSC4140_DELAY_TOO_LARGE",
             channel.json_body.get("errcode"),
             channel.json_body,
         )