--- a/ping_common.c	2014-11-11 00:02:07.000000000 +0000
+++ b/ping_common.c	2014-11-11 09:04:06.699021939 +0000
@@ -1016,14 +1016,17 @@
 	}
 	putchar('\n');
 
 	if (nreceived && timing) {
 		long tmdev;
+		long count = nreceived + nrepeats;
 
-		tsum /= nreceived + nrepeats;
-		tsum2 /= nreceived + nrepeats;
-		tmdev = llsqrt(tsum2 - tsum * tsum);
+		// mdev = sqrt((tsum2/count) - (tsum/count)*(tsum2/count))
+		// However, we must be careful about rounding!
+		tmdev = llsqrt((tsum2 * count - tsum * tsum) / (count * count));
+		tsum2 /= count;
+		tsum /= count;
 
 		printf("rtt min/avg/max/mdev = %ld.%03ld/%lu.%03ld/%ld.%03ld/%ld.%03ld ms",
 		       (long)tmin/1000, (long)tmin%1000,
 		       (unsigned long)(tsum/1000), (long)(tsum%1000),
 		       (long)tmax/1000, (long)tmax%1000,