diff --git a/racket/src/ChezScheme/LOG b/racket/src/ChezScheme/LOG
index fb55caef59..79c1b5912d 100644
--- a/racket/src/ChezScheme/LOG
+++ b/racket/src/ChezScheme/LOG
@@ -2135,3 +2135,8 @@
 - added textual-output-port checks for record-writer write argument
     print.ss,
     record.ms, root-experr*
+- now using 64-bit arithmetic for seconds in S_condition_wait to
+  prevent a potential 2038 bug, at least on platforms where time_t
+  is 64 bits.  also now rounding rather than truncating nanoseconds
+  in the coversion to milliseconds on Windows.
+    thread.c
diff --git a/racket/src/ChezScheme/c/thread.c b/racket/src/ChezScheme/c/thread.c
index 39c0c8d7bb..92a58f565a 100644
--- a/racket/src/ChezScheme/c/thread.c
+++ b/racket/src/ChezScheme/c/thread.c
@@ -456,11 +456,11 @@ void S_condition_free(c) s_thread_cond_t *c; {
 
 #ifdef FEATURE_WINDOWS
 
-static inline int s_thread_cond_timedwait(s_thread_cond_t *cond, s_thread_mutex_t *mutex, int typeno, long sec, long nsec) {
+static inline int s_thread_cond_timedwait(s_thread_cond_t *cond, s_thread_mutex_t *mutex, int typeno, I64 sec, long nsec) {
   if (typeno == time_utc) {
     struct timespec now;
     S_gettime(time_utc, &now);
-    sec -= (long)now.tv_sec;
+    sec -= now.tv_sec;
     nsec -= now.tv_nsec;
     if (nsec < 0) {
       sec -= 1;
@@ -471,7 +471,7 @@ static inline int s_thread_cond_timedwait(s_thread_cond_t *cond, s_thread_mutex_
     sec = 0;
     nsec = 0;
   }
-  if (SleepConditionVariableCS(cond, mutex, sec*1000 + nsec/1000000)) {
+  if (SleepConditionVariableCS(cond, mutex, (DWORD)(sec*1000 + (nsec+500000)/1000000))) {
     return 0;
   } else if (GetLastError() == ERROR_TIMEOUT) {
     return ETIMEDOUT;
@@ -482,12 +482,12 @@ static inline int s_thread_cond_timedwait(s_thread_cond_t *cond, s_thread_mutex_
 
 #else /* FEATURE_WINDOWS */
 
-static inline int s_thread_cond_timedwait(s_thread_cond_t *cond, s_thread_mutex_t *mutex, int typeno, long sec, long nsec) {
+static inline int s_thread_cond_timedwait(s_thread_cond_t *cond, s_thread_mutex_t *mutex, int typeno, I64 sec, long nsec) {
   struct timespec t;
   if (typeno == time_duration) {
     struct timespec now;
     S_gettime(time_utc, &now);
-    t.tv_sec = now.tv_sec + sec;
+    t.tv_sec = (time_t)(now.tv_sec + sec);
     t.tv_nsec = now.tv_nsec + nsec;
     if (t.tv_nsec >= 1000000000) {
       t.tv_sec += 1;
@@ -509,7 +509,7 @@ IBOOL S_condition_wait(c, m, t) s_thread_cond_t *c; scheme_mutex_t *m; ptr t; {
   s_thread_t self = s_thread_self();
   iptr count;
   INT typeno;
-  long sec;
+  I64 sec;
   long nsec;
   INT status;
   IBOOL is_collect;
@@ -524,7 +524,7 @@ IBOOL S_condition_wait(c, m, t) s_thread_cond_t *c; scheme_mutex_t *m; ptr t; {
   if (t != Sfalse) {
     /* Keep in sync with ts record in s/date.ss */
     typeno = Sinteger32_value(Srecord_ref(t,0));
-    sec = Sinteger32_value(Scar(Srecord_ref(t,1)));
+    sec = Sinteger64_value(Scar(Srecord_ref(t,1)));
     nsec = Sinteger32_value(Scdr(Srecord_ref(t,1)));
   } else {
     typeno = 0;