diff --git a/shadowsocks-csharp/Encrypt/OpenSSLEncryptor.cs b/shadowsocks-csharp/Encrypt/OpenSSLEncryptor.cs
index 7abdb375..bcea60a3 100755
--- a/shadowsocks-csharp/Encrypt/OpenSSLEncryptor.cs
+++ b/shadowsocks-csharp/Encrypt/OpenSSLEncryptor.cs
@@ -40,7 +40,7 @@ namespace Shadowsocks.Encrypt
                 outlength = length + ivLen;
                 OpenSSL.EVP_CipherUpdate(_encryptCtx, tempbuf, out outlength, buf, length);
                 outlength = length + ivLen;
-                Buffer.BlockCopy(tempbuf, 0, outbuf, ivLen, outlength);
+                Buffer.BlockCopy(tempbuf, 0, outbuf, ivLen, length);
             }
             else
             {
diff --git a/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs b/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs
index 68293a8a..b959565e 100755
--- a/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs
+++ b/shadowsocks-csharp/Encrypt/PolarSSLEncryptor.cs
@@ -192,7 +192,7 @@ namespace Shadowsocks.Encrypt
                                 break;
                         }
                         outlength = length + ivLen;
-                        Buffer.BlockCopy(tempbuf, 0, outbuf, ivLen, outlength);
+                        Buffer.BlockCopy(tempbuf, 0, outbuf, ivLen, length);
                     }
                 }
             }