diff --git a/stubs/psycopg2/psycopg2/sql.pyi b/stubs/psycopg2/psycopg2/sql.pyi
index be30d720f..923e0ef90 100644
--- a/stubs/psycopg2/psycopg2/sql.pyi
+++ b/stubs/psycopg2/psycopg2/sql.pyi
@@ -2,7 +2,7 @@ from typing import Any
 
 class Composable:
     def __init__(self, wrapped) -> None: ...
-    def as_string(self, context) -> None: ...
+    def as_string(self, context) -> str: ...
     def __add__(self, other): ...
     def __mul__(self, n): ...
     def __eq__(self, other): ...