diff --git a/src/calibre/gui2/tweak_book/completion/utils.py b/src/calibre/gui2/tweak_book/completion/utils.py
index a1687a8116..919269df4e 100644
--- a/src/calibre/gui2/tweak_book/completion/utils.py
+++ b/src/calibre/gui2/tweak_book/completion/utils.py
@@ -21,3 +21,6 @@ class DataError(Exception):
     def __init__(self, tb, msg=None):
         Exception.__init__(self, msg or _('Failed to get completion data'))
         self.tb = tb
+
+    def traceback(self):
+        return unicode(self) + '\n' + self.tb
diff --git a/src/calibre/gui2/tweak_book/completion/worker.py b/src/calibre/gui2/tweak_book/completion/worker.py
index d97f74a75a..84a8569031 100644
--- a/src/calibre/gui2/tweak_book/completion/worker.py
+++ b/src/calibre/gui2/tweak_book/completion/worker.py
@@ -14,6 +14,7 @@ from collections import namedtuple
 
 from calibre.constants import iswindows
 from calibre.gui2.tweak_book.completion.basic import Request
+from calibre.gui2.tweak_book.completion.utils import DataError
 from calibre.utils.ipc import eintr_retry_call
 
 COMPLETION_REQUEST = 'completion request'
@@ -179,6 +180,8 @@ def main(control_conn, data_conn):
             break
         try:
             ans, tb = handle_control_request(request, data_conn), None
+        except DataError as err:
+            ans, tb = None, err.traceback()
         except Exception:
             import traceback
             ans, tb = None, traceback.format_exc()