diff --git a/sys/kern/ktime.c b/sys/kern/ktime.c
index 41fc445..3cb0103 100644
--- a/sys/kern/ktime.c
+++ b/sys/kern/ktime.c
@@ -194,7 +194,12 @@ KTime_GetEpochNS()
 
     Spinlock_Lock(&ktimeLock);
     tscDiff = Time_GetTSC() - ktimeLastTSC;
-    epoch = (ktimeLastEpoch * 1000000000) + (tscDiff * 1000000000 / ticksPerSecond);
+    /*
+     * This is ugly but it avoids overflowing tscDiff to time computation.  
+     * Note that the bottom bits of ticksPerSecond are not significant so it is 
+     * okay to discard them.
+     */
+    epoch = (ktimeLastEpoch * 1000000000ULL) + (tscDiff * 1000000ULL / ticksPerSecond * 1000ULL);
     Spinlock_Unlock(&ktimeLock);
 
     return epoch;