diff --git a/Include/warnings.h b/Include/warnings.h
index 7553a25..b7db681 100644
--- a/Include/warnings.h
+++ b/Include/warnings.h
@@ -20,7 +20,7 @@
 PyAPI_FUNC(int) PyErr_WarnExplicit(
     PyObject *category,
     const char *message,        /* UTF-8 encoded string */
-    const char *filename,       /* UTF-8 encoded string */
+    const char *filename,       /* decoded from the filesystem encoding */
     int lineno,
     const char *module,         /* UTF-8 encoded string */
     PyObject *registry);