diff --git a/piker/exchange/_ems.py b/piker/exchange/_ems.py
index 291e9c5f..5ebfee4a 100644
--- a/piker/exchange/_ems.py
+++ b/piker/exchange/_ems.py
@@ -378,7 +378,10 @@ async def process_broker_trades(
                 oid = paper['oid']
 
             else:
-                msg['external']
+                msg.get('external')
+                if not msg:
+                    log.error(f"Unknown trade event {event}")
+
                 continue
 
         resp = {