diff --git a/sphinx/application.py b/sphinx/application.py
index 9cd3d856bd4..9636ae0e861 100644
--- a/sphinx/application.py
+++ b/sphinx/application.py
@@ -1134,6 +1134,7 @@ def setup(app):
                 type='app',
                 subtype='add_directive',
             )
+            return
 
         docutils.register_directive(name, cls)