diff --git a/src/calibre/gui2/open_with.py b/src/calibre/gui2/open_with.py
index 7f77c43297..042b3e7bd1 100644
--- a/src/calibre/gui2/open_with.py
+++ b/src/calibre/gui2/open_with.py
@@ -155,7 +155,7 @@ elif isosx:
         return sort_key(entry.get('name') or '')
 
     def finalize_entry(entry):
-        entry['extensions'] = tuple(entry['extensions'])
+        entry['extensions'] = tuple(entry.get('extensions', ()))
         data = get_icon(entry.pop('icon_file', None), as_data=True, pixmap_to_data=pixmap_to_data)
         if data:
             entry['icon_data'] = data