diff --git a/harness/assert.js b/harness/assert.js
index 384b8e8f0e0df971145dd2f8b4a8da7228a86d4a..5fbc12254106940016c47fa72cba23af6d706fd7 100644
--- a/harness/assert.js
+++ b/harness/assert.js
@@ -88,8 +88,8 @@ assert.throws = function (expectedErrorConstructor, func, message) {
 };
 
 assert.throws.early = function(err, code) {
-  let wrappedCode = 'function wrapperFn() { ' + code + ' }';
-  let ieval = eval;
+  var wrappedCode = 'function wrapperFn() { ' + code + ' }';
+  var ieval = eval;
 
   assert.throws(err, function() { Function(wrappedCode); }, 'Function: ' + code);
 };