Issue #25923: Added more const qualifiers to signatures of static and private functions.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 6bb2200..16f8cdf 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -659,7 +659,7 @@
 
 /* Sets the current error to BlockingIOError */
 static void
-_set_BlockingIOError(char *msg, Py_ssize_t written)
+_set_BlockingIOError(const char *msg, Py_ssize_t written)
 {
     PyObject *err;
     PyErr_Clear();