diff --git a/src/calibre/gui2/tweak_book/boss.py b/src/calibre/gui2/tweak_book/boss.py
index 3c8884fe6f..ce2f89408d 100644
--- a/src/calibre/gui2/tweak_book/boss.py
+++ b/src/calibre/gui2/tweak_book/boss.py
@@ -233,7 +233,7 @@ class Boss(QObject):
         if not syntax:
             return error_dialog(
                 self.gui, _('Unsupported file format'),
-                _('Editing of files of type %s is not supported' % mime), show=True)
+                _('Editing files of type %s is not supported' % mime), show=True)
         self.edit_file(name, syntax)
 
     def do_editor_undo(self):