diff --git a/ChangeLog b/ChangeLog
index 246d913890..f02f9dc31a 100755
--- a/ChangeLog
+++ b/ChangeLog
@@ -11058,4 +11058,5 @@
 	* drivers/discrete/userled_lower.c:  Add a generic lower-half user LED
 	  driver that may be used by any board that supports the standard
 	  board user LED interfaces (2015-11-01).
-
+	* sched/clock: Fix error in clock_timespec_subtract().  Found by Lok
+	  (2015-11-03).
diff --git a/arch b/arch
index 7526685e83..b763efbe64 160000
--- a/arch
+++ b/arch
@@ -1 +1 @@
-Subproject commit 7526685e83229a7249d739b15bb1844eee9fce8e
+Subproject commit b763efbe64b84ff1cefdd428c7a3d7b7b69f1c9b
diff --git a/sched/clock/clock_timespec_subtract.c b/sched/clock/clock_timespec_subtract.c
index c47ea35562..c02dc35538 100644
--- a/sched/clock/clock_timespec_subtract.c
+++ b/sched/clock/clock_timespec_subtract.c
@@ -83,7 +83,7 @@ void clock_timespec_subtract(FAR const struct timespec *ts1,
     }
   else
     {
-      sec = ts1->tv_sec + ts2->tv_sec;
+      sec = ts1->tv_sec - ts2->tv_sec;
       if (ts1->tv_nsec < ts2->tv_nsec)
         {
           nsec = (ts1->tv_nsec + NSEC_PER_SEC) - ts2->tv_nsec;