diff --git a/pkg/throttle/throttle.go b/pkg/throttle/throttle.go
index 6c6d3a44f..5c6972346 100644
--- a/pkg/throttle/throttle.go
+++ b/pkg/throttle/throttle.go
@@ -128,8 +128,8 @@ func (c *conn) Write(p []byte) (n int, err error) {
 
 func (c *conn) Read(p []byte) (n int, err error) {
 	const max = 1024
-	if len(p) > sz {
-		p = p[:sz]
+	if len(p) > max {
+		p = p[:max]
 	}
 	n, err = c.Conn.Read(p)
 	time.Sleep(c.Down.byteTime(n))