diff --git a/lib/6to5/transformation/transformers/es6-rest-parameters.js b/lib/6to5/transformation/transformers/es6-rest-parameters.js
index aab79e8103..68dfdd0ae8 100644
--- a/lib/6to5/transformation/transformers/es6-rest-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-rest-parameters.js
@@ -19,15 +19,17 @@ exports.Function = function (node, parent, file) {
   var len = file.generateUidIdentifier("len");
 
   var arrKey = key;
+  var arrLen = len;
   if (node.params.length) {
     // this method has additional params, so we need to subtract
     // the index of the current argument position from the
     // position in the array that we want to populate
     arrKey = t.binaryExpression("-", key, start);
-  }
 
-  var arrLen = len;
-  if (node.params.length) {
+    // we need to work out the size of the array that we're
+    // going to store all the rest parameters in, if there
+    // are less arguments than params then the array can be
+    // constructed with <1 which will cause an error
     arrLen = t.conditionalExpression(
       t.binaryExpression(">", len, start),
       t.binaryExpression("-", len, start),