diff --git a/IPython/frontend/qt/kernelmanager.py b/IPython/frontend/qt/kernelmanager.py
index 32a7388..c47b489 100644
--- a/IPython/frontend/qt/kernelmanager.py
+++ b/IPython/frontend/qt/kernelmanager.py
@@ -46,6 +46,7 @@ class QtXReqSocketChannel(SocketChannelQObject, XReqSocketChannel):
     execute_reply = QtCore.Signal(object)
     complete_reply = QtCore.Signal(object)
     object_info_reply = QtCore.Signal(object)
+    history_tail_reply = QtCore.Signal(object)
 
     # Emitted when the first reply comes back.
     first_reply = QtCore.Signal()