diff --git a/src/calibre/gui2/open_with.py b/src/calibre/gui2/open_with.py
index 081293147e..c9f38cea0d 100644
--- a/src/calibre/gui2/open_with.py
+++ b/src/calibre/gui2/open_with.py
@@ -210,7 +210,7 @@ elif ismacos:
             if os.path.isdir(ans):
                 app = get_bundle_data(ans)
                 if app is None:
-                    error_dialog(parent, _('Invalid Application'), _(
+                    error_dialog(parent, _('Invalid application'), _(
                         '%s is not a valid macOS application bundle.') % ans, show=True)
                     return
                 return app