diff --git a/tractor/_portal.py b/tractor/_portal.py
index f310643..378f6a2 100644
--- a/tractor/_portal.py
+++ b/tractor/_portal.py
@@ -69,10 +69,10 @@ def _unwrap_msg(
     __tracebackhide__ = True
     try:
         return msg['return']
-    except KeyError:
+    except KeyError as ke:
         # internal error should never get here
         assert msg.get('cid'), "Received internal error at portal?"
-        raise unpack_error(msg, channel) from None
+        raise unpack_error(msg, channel) from ke
 
 
 class Portal: