diff --git a/cibuildwheel/projectfiles.py b/cibuildwheel/projectfiles.py
index 196314601..3117486fe 100644
--- a/cibuildwheel/projectfiles.py
+++ b/cibuildwheel/projectfiles.py
@@ -50,7 +50,7 @@ def visit_keyword(self, node: ast.keyword) -> None:
         )
 
         match node:
-            case ast.keyword(arg="python_requires", value=ast.Constant(value=str(version))):
+            case ast.keyword(arg="python_requires", value=ast.Constant(value=str() as version)):
                 if unnested or name_main_unnested:
                     self.requires_python = version