diff --git a/Python/ast.c b/Python/ast.c
index d2f063b..e395c5a 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -3305,7 +3305,7 @@
     int quote = Py_CHARMASK(*s);
     int rawmode = 0;
     int need_encoding;
-    if (isalpha(quote)) {
+    if (Py_ISALPHA(quote)) {
         if (quote == 'b' || quote == 'B') {
             quote = *++s;
             *bytesmode = 1;