diff --git a/src/calibre/gui2/convert/regex_builder.py b/src/calibre/gui2/convert/regex_builder.py
index 07c63de93a..58c4efbe1d 100644
--- a/src/calibre/gui2/convert/regex_builder.py
+++ b/src/calibre/gui2/convert/regex_builder.py
@@ -126,6 +126,9 @@ class RegexEdit(QWidget, Ui_Edit):
     def set_db(self, db):
         self.db = db
 
+    def break_cycles(self):
+        self.db = None
+
     @property
     def text(self):
         return unicode(self.edit.text())
diff --git a/src/calibre/gui2/convert/structure_detection.py b/src/calibre/gui2/convert/structure_detection.py
index 1797a76760..bf360f5315 100644
--- a/src/calibre/gui2/convert/structure_detection.py
+++ b/src/calibre/gui2/convert/structure_detection.py
@@ -43,8 +43,8 @@ class StructureDetectionWidget(Widget, Ui_Form):
 
     def break_cycles(self):
         Widget.break_cycles(self)
-        self.opt_header_regex.db = None
-        self.opt_footer_regex.db = None
+        self.opt_header_regex.break_cycles()
+        self.opt_footer_regex.break_cycles()
 
     def pre_commit_check(self):
         for x in ('header_regex', 'footer_regex'):