diff -r 4c7feafa28c3 rpython/translator/c/src/thread_nt.c
--- a/rpython/translator/c/src/thread_nt.c	Wed Apr 10 07:50:25 2013 -0700
+++ b/rpython/translator/c/src/thread_nt.c	Thu Apr 11 09:23:31 2013 -0700
@@ -23,7 +23,7 @@
 	HANDLE done;
 } callobj;
 
-static long _pypythread_stacksize = 0;
+static unsigned _pypythread_stacksize = 0;
 
 /*
  * Return the thread Id instead of an handle. The Id is said to uniquely
@@ -48,7 +48,7 @@
 
 long RPyThreadStart(void (*func)(void))
 {
-	unsigned long rv;
+	uintptr_t rv;
 	callobj obj;
 
 	obj.id = -1;	/* guilty until proved innocent */
@@ -58,7 +58,7 @@
 		return -1;
 
 	rv = _beginthread(bootstrap, _pypythread_stacksize, &obj);
-	if (rv == (unsigned long)-1) {
+	if (rv == (uintptr_t)-1) {
 		/* I've seen errno == EAGAIN here, which means "there are
 		 * too many threads".
 		 */
@@ -84,7 +84,7 @@
 	return _pypythread_stacksize;
 }
 
-long RPyThreadSetStackSize(long newsize)
+long RPyThreadSetStackSize(unsigned newsize)
 {
 	if (newsize == 0) {    /* set to default */
 		_pypythread_stacksize = 0;
diff -r 4c7feafa28c3 rpython/translator/c/src/thread_nt.h
--- a/rpython/translator/c/src/thread_nt.h	Wed Apr 10 07:50:25 2013 -0700
+++ b/rpython/translator/c/src/thread_nt.h	Thu Apr 11 09:23:31 2013 -0700
@@ -18,5 +18,5 @@
 					RPY_TIMEOUT_T timeout, int intr_flag);
 void RPyThreadReleaseLock(struct RPyOpaque_ThreadLock *lock);
 long RPyThreadGetStackSize(void);
-long RPyThreadSetStackSize(long);
+long RPyThreadSetStackSize(unsigned);