diff --git a/blktrace.c b/blktrace.c
index 864e9dc..1669fe5 100644
--- a/blktrace.c
+++ b/blktrace.c
@@ -100,6 +100,7 @@
 
 	rw = (t->action & BLK_TC_ACT(BLK_TC_WRITE)) != 0;
 	ios[rw]++;
+	td->o.size += t->bytes;
 	store_ipo(td, t->sector, t->bytes, rw, ttime);
 }
 
@@ -120,6 +121,8 @@
 		return 1;
 	}
 
+	td->o.size = 0;
+
 	ios[0] = ios[1] = 0;
 	ttime = 0;
 	do {