diff --git a/src/xterm.js b/src/xterm.js
index b6c659c3..b92736a9 100644
--- a/src/xterm.js
+++ b/src/xterm.js
@@ -614,7 +614,7 @@ Terminal.prototype.open = function(parent) {
   }
   this.parent.appendChild(this.element);
 
-  this.charMeasure = new CharMeasure(this.rowContainer);
+  this.charMeasure = new CharMeasure(this.helperContainer);
   this.charMeasure.on('charsizechanged', function () {
     self.updateCharSizeCSS();
   });