diff --git a/proxy/shadowsocks/config.go b/proxy/shadowsocks/config.go
index 7da5e0e39a..ef592a2faf 100644
--- a/proxy/shadowsocks/config.go
+++ b/proxy/shadowsocks/config.go
@@ -74,7 +74,7 @@ func (v *AesCfb) KeySize() int {
 }
 
 func (v *AesCfb) IVSize() int {
-	return v.KeyBytes
+	return 16
 }
 
 func (v *AesCfb) NewEncodingStream(key []byte, iv []byte) (cipher.Stream, error) {