diff --git a/src/calibre/gui2/tweak_book/editor/syntax/base.py b/src/calibre/gui2/tweak_book/editor/syntax/base.py
index 5661781480..f0649a7d58 100644
--- a/src/calibre/gui2/tweak_book/editor/syntax/base.py
+++ b/src/calibre/gui2/tweak_book/editor/syntax/base.py
@@ -41,7 +41,6 @@ class SyntaxHighlighter(QSyntaxHighlighter):
         return SimpleState(max(0, num))
 
     def rehighlight(self):
-        self.outlineexplorer_data = {}
         QApplication.setOverrideCursor(QCursor(Qt.WaitCursor))
         QSyntaxHighlighter.rehighlight(self)
         QApplication.restoreOverrideCursor()