diff --git a/addon/runmode/runmode.node.js b/addon/runmode/runmode.node.js
index 01d08ffed89e727e7ea7a2f5ba676b0b61fdfb5c..833bd6ed76040216624251095e3e9121730499ea 100644
--- a/addon/runmode/runmode.node.js
+++ b/addon/runmode/runmode.node.js
@@ -94,7 +94,7 @@ StringStream.prototype = {
     finally { this.lineStart -= n; }
   },
   lookAhead: function(n) {
-    let line = this.context.line + n
+    var line = this.context.line + n
     return line >= this.context.lines.length ? null : this.context.lines[line]
   }
 };