diff --git a/core/collection/rollingwindow.go b/core/collection/rollingwindow.go
index 804fda3e..c9f45aaf 100644
--- a/core/collection/rollingwindow.go
+++ b/core/collection/rollingwindow.go
@@ -74,27 +74,29 @@ func (rw *RollingWindow) span() int {
 
 func (rw *RollingWindow) updateOffset() {
 	span := rw.span()
-	if span > 0 {
-		offset := rw.offset
-		start := offset + 1
-		steps := start + span
-		var remainder int
-		if steps > rw.size {
-			remainder = steps - rw.size
-			steps = rw.size
-		}
-
-		// reset expired buckets
-		for i := start; i < steps; i++ {
-			rw.win.resetBucket(i)
-		}
-		for i := 0; i < remainder; i++ {
-			rw.win.resetBucket(i)
-		}
-
-		rw.offset = (offset + span) % rw.size
-		rw.lastTime = timex.Now()
+	if span <= 0 {
+		return
 	}
+
+	offset := rw.offset
+	start := offset + 1
+	steps := start + span
+	var remainder int
+	if steps > rw.size {
+		remainder = steps - rw.size
+		steps = rw.size
+	}
+
+	// reset expired buckets
+	for i := start; i < steps; i++ {
+		rw.win.resetBucket(i)
+	}
+	for i := 0; i < remainder; i++ {
+		rw.win.resetBucket(i)
+	}
+
+	rw.offset = (offset + span) % rw.size
+	rw.lastTime = timex.Now()
 }
 
 type Bucket struct {