diff --git a/src/calibre/gui2/tools.py b/src/calibre/gui2/tools.py
index 14d94afa89..e2136cf0ed 100644
--- a/src/calibre/gui2/tools.py
+++ b/src/calibre/gui2/tools.py
@@ -122,7 +122,7 @@ def convert_single_ebook(parent, db, book_ids, auto_conversion=False,  # {{{
                 (
                     _('Could not convert the book because no supported source format was found')
                     if len(res) == 1 else
-                    _('Could not convert {num} of {tot} books, because no supported source formats were found.'),
+                    _('Could not convert {num} of {tot} books, because no supported source formats were found.')
                 ).format(num=len(res), tot=total),
                 msg).exec_()