On Windows, need #include <windows.h>; and it's MS_WINDOWS, not MS_WIN32.
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index d2bbff7..1c2c793 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -62,6 +62,10 @@
#include "thread.h"
#endif
+#ifdef MS_WINDOWS
+#include <windows.h>
+#endif
+
#ifdef macintosh
#define MAC_TCL
#include "myselect.h"
@@ -258,7 +262,7 @@
/**** Utils ****/
#ifdef WITH_THREAD
-#ifndef MS_WIN32
+#ifndef MS_WINDOWS
/* Millisecond sleep() for Unix platforms. */
static void
@@ -272,7 +276,7 @@
t.tv_usec = (milli%1000) * 1000;
select(0, (fd_set *)0, (fd_set *)0, (fd_set *)0, &t);
}
-#endif /* MS_WIN32 */
+#endif /* MS_WINDOWS */
#endif /* WITH_THREAD */