diff --git a/lib/util.js b/lib/util.js
index da2b092..2029cc9 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -203,7 +203,7 @@ exports.packUInt32BE = function(num){
 exports.packInt64LE = function(num){
     var buff = new Buffer(8);
     buff.writeUInt32LE(num % Math.pow(2, 32), 0);
-    buff.writeUInt32LE(Math.floor(num / Math.pow(2, 32)), 5);
+    buff.writeUInt32LE(Math.floor(num / Math.pow(2, 32)), 4);
     return buff;
 };