diff --git a/flask/app.py b/flask/app.py
index 1ad669e3..adc017d0 100644
--- a/flask/app.py
+++ b/flask/app.py
@@ -466,7 +466,7 @@ class Flask(_PackageBoundObject):
         if self.import_name == '__main__':
             fn = getattr(sys.modules['__main__'], '__file__', None)
             if fn is None:
-                return 'unknown'
+                return '__main__'
             return os.path.splitext(os.path.basename(fn))[0]
         return self.import_name