diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index f3a9f5c..adb04c0 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -484,6 +484,10 @@
 	Py_UNICODE *value;
 	int len;
 
+	/* issue4122: Undefined reference to _Py_ascii_whitespace on Windows */
+	/* Just use the macro and check that it compiles */
+	int x = Py_UNICODE_ISSPACE(25);
+
         tuple = PyTuple_New(1);
         if (tuple == NULL)
         	return NULL;