diff --git a/src/calibre/gui2/convert/regex_builder.py b/src/calibre/gui2/convert/regex_builder.py
index bdcbe3356d..bdd219d733 100644
--- a/src/calibre/gui2/convert/regex_builder.py
+++ b/src/calibre/gui2/convert/regex_builder.py
@@ -166,6 +166,8 @@ class RegexEdit(QWidget, Ui_Edit):
 
     def builder(self):
         bld = RegexBuilder(self.db, self.book_id, self.edit.text(), self)
+        if bld.cancelled:
+            return
         if bld.exec_() == bld.Accepted:
             self.edit.setText(bld.regex.text())