diff --git a/Python/condvar.h b/Python/condvar.h
--- a/Python/condvar.h
+++ b/Python/condvar.h
@@ -60,7 +60,7 @@
 #include <pthread.h>
 
 #define PyCOND_ADD_MICROSECONDS(tv, interval) \
-do { \
+do { /* TODO: add overflow and truncation checks */ \
     tv.tv_usec += (long) interval; \
     tv.tv_sec += tv.tv_usec / 1000000; \
     tv.tv_usec %= 1000000; \
@@ -89,7 +89,7 @@
 
 /* return 0 for success, 1 on timeout, -1 on error */
 Py_LOCAL_INLINE(int)
-PyCOND_TIMEDWAIT(PyCOND_T *cond, PyMUTEX_T *mut, long us)
+PyCOND_TIMEDWAIT(PyCOND_T *cond, PyMUTEX_T *mut, Py_LONG_LONG us)
 {
     int r;
     struct timespec ts;
@@ -270,9 +270,9 @@
 }
 
 Py_LOCAL_INLINE(int)
-PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, long us)
+PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, Py_LONG_LONG us)
 {
-    return _PyCOND_WAIT_MS(cv, cs, us/1000);
+    return _PyCOND_WAIT_MS(cv, cs, (DWORD)(us/1000));
 }
 
 Py_LOCAL_INLINE(int)
@@ -363,9 +363,9 @@
  * 2 to indicate that we don't know.
  */
 Py_LOCAL_INLINE(int)
-PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, long us)
+PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, Py_LONG_LONG us)
 {
-    return SleepConditionVariableSRW(cv, cs, us/1000, 0) ? 2 : -1;
+    return SleepConditionVariableSRW(cv, cs, (DWORD)(us/1000), 0) ? 2 : -1;
 }
 
 Py_LOCAL_INLINE(int)
diff --git a/Python/thread_nt.h b/Python/thread_nt.h
--- a/Python/thread_nt.h
+++ b/Python/thread_nt.h
@@ -77,7 +77,7 @@
         /* wait at least until the target */
         DWORD now, target = GetTickCount() + milliseconds;
         while (mutex->locked) {
-            if (PyCOND_TIMEDWAIT(&mutex->cv, &mutex->cs, milliseconds*1000) < 0) {
+            if (PyCOND_TIMEDWAIT(&mutex->cv, &mutex->cs, (Py_LONG_LONG)milliseconds*1000) < 0) {
                 result = WAIT_FAILED;
                 break;
             }