diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index f1b4455..a4057fd 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -22,7 +22,7 @@
 
  */
 #define Py_UNICODE_ISSPACE(ch) \
-    ((ch) < 128U ? _Py_ascii_whitespace[(ch)] : _PyUnicode_IsWhitespace(ch))
+    ((Py_UCS4)(ch) < 128U ? _Py_ascii_whitespace[(ch)] : _PyUnicode_IsWhitespace(ch))
 
 #define Py_UNICODE_ISLOWER(ch) _PyUnicode_IsLowercase(ch)
 #define Py_UNICODE_ISUPPER(ch) _PyUnicode_IsUppercase(ch)