1 files changed, 4 insertions, 0 deletions
diff --git a/synapse/storage/databases/main/deviceinbox.py b/synapse/storage/databases/main/deviceinbox.py
index 042d595ea0..47ba1eeff4 100644
--- a/synapse/storage/databases/main/deviceinbox.py
+++ b/synapse/storage/databases/main/deviceinbox.py
@@ -888,6 +888,10 @@ class DeviceInboxWorkerStore(SQLBaseStore):
                     retcol="device_id",
                 )
 
+                if len(devices) > 1000:
+                    logger.warn("ignoring wildcard to-device messages to %i devices", len(devices))
+                    continue
+
                 message_json = json_encoder.encode(messages_by_device["*"])
                 for device_id in devices:
                     # Add the message for all devices for this user on this