diff --git a/ChangeLog b/ChangeLog
index 82880f6a8b..a3516edd42 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Fri May 21 01:06:05 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* thread.c (subtract_tv): if the rest is zero, should finish waiting
+	  immediately.
+
+	* win32/win32.c (subtract): ditto.
+	  based on a patch from Roger Pack in [ruby-core:27957].
+
 Thu May 20 22:49:04 2010  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* re.c (rb_reg_s_union_m): update rdoc.  [ruby-dev:41354]
diff --git a/thread.c b/thread.c
index f6b3b67df4..1956721da7 100644
--- a/thread.c
+++ b/thread.c
@@ -2411,6 +2411,9 @@ cmp_tv(const struct timeval *a, const struct timeval *b)
 static int
 subtract_tv(struct timeval *rest, const struct timeval *wait)
 {
+    if (rest->tv_sec < wait->tv_sec) {
+	return 0;
+    }
     while (rest->tv_usec < wait->tv_usec) {
 	if (rest->tv_sec <= wait->tv_sec) {
 	    return 0;
@@ -2420,7 +2423,7 @@ subtract_tv(struct timeval *rest, const struct timeval *wait)
     }
     rest->tv_sec -= wait->tv_sec;
     rest->tv_usec -= wait->tv_usec;
-    return 1;
+    return rest->tv_sec != 0 || rest->tv_usec != 0;
 }
 #endif
 
diff --git a/win32/win32.c b/win32/win32.c
index 62498cb47c..506a960d36 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -2471,7 +2471,7 @@ subtract(struct timeval *rest, const struct timeval *wait)
     }
     rest->tv_sec -= wait->tv_sec;
     rest->tv_usec -= wait->tv_usec;
-    return 1;
+    return rest->tv_sec != 0 || rest->tv_usec != 0;
 }
 
 static inline int