diff --git a/src/time/sleep_test.go b/src/time/sleep_test.go
index 7bad49f413..3d00b6803c 100644
--- a/src/time/sleep_test.go
+++ b/src/time/sleep_test.go
@@ -63,7 +63,7 @@ func TestSleep(t *testing.T) {
 	start := Now()
 	Sleep(delay)
 	delayadj := adjustDelay(t, delay)
-	duration := Now().Sub(start)
+	duration := Since(start)
 	if duration < delayadj {
 		t.Fatalf("Sleep(%s) slept for only %s", delay, duration)
 	}
@@ -289,7 +289,7 @@ func TestAfter(t *testing.T) {
 	start := Now()
 	end := <-After(delay)
 	delayadj := adjustDelay(t, delay)
-	if duration := Now().Sub(start); duration < delayadj {
+	if duration := Since(start); duration < delayadj {
 		t.Fatalf("After(%s) slept for only %d ns", delay, duration)
 	}
 	if min := start.Add(delayadj); end.Before(min) {