diff --git a/src/flask/cli.py b/src/flask/cli.py
index f66b2393..713d2b59 100644
--- a/src/flask/cli.py
+++ b/src/flask/cli.py
@@ -60,7 +60,7 @@ def find_best_app(script_info, module):
         )
 
     # Search for app factory functions.
-    for attr_name in {"create_app", "make_app"}:
+    for attr_name in ("create_app", "make_app"):
         app_factory = getattr(module, attr_name, None)
 
         if inspect.isfunction(app_factory):