diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index f1b44554e3078d..a4057fd2a13edb 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)
diff --git a/Misc/NEWS.d/next/C API/2021-01-27-10-27-47.bpo-43030.loDcD_.rst b/Misc/NEWS.d/next/C API/2021-01-27-10-27-47.bpo-43030.loDcD_.rst
new file mode 100644
index 00000000000000..7a432522db8a12
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2021-01-27-10-27-47.bpo-43030.loDcD_.rst	
@@ -0,0 +1,2 @@
+Fixed a compiler warning in :c:func:`Py_UNICODE_ISSPACE()` on platforms with
+signed ``wchar_t``.