diff --git a/fastapi/params.py b/fastapi/params.py
index 8f5601dd3..2740b5824 100644
--- a/fastapi/params.py
+++ b/fastapi/params.py
@@ -783,4 +783,7 @@ class Security(Depends):
         use_cache: bool = True,
     ):
         super().__init__(dependency=dependency, use_cache=use_cache)
-        self.scopes = scopes or []
+        if isinstance(scopes, str):
+            self.scopes = [scopes]
+        else:
+            self.scopes = scopes or []