diff --git a/src/calibre/gui2/tweak_book/editor/text.py b/src/calibre/gui2/tweak_book/editor/text.py
index d2be408e3a..7f90600b2f 100644
--- a/src/calibre/gui2/tweak_book/editor/text.py
+++ b/src/calibre/gui2/tweak_book/editor/text.py
@@ -220,7 +220,7 @@ class TextEdit(PlainTextEdit):
         sclass = {'html':HTMLSmarts, 'xml':HTMLSmarts, 'css':CSSSmarts}.get(syntax, None)
         if sclass is not None:
             self.smarts = sclass(self)
-        self.setPlainText(unicodedata.normalize('NFC', text))
+        self.setPlainText(unicodedata.normalize('NFC', unicode(text)))
         if process_template and QPlainTextEdit.find(self, '%CURSOR%'):
             c = self.textCursor()
             c.insertText('')