diff --git a/lib/ace/test/mockrenderer.js b/lib/ace/test/mockrenderer.js
index eefbd08f..799772f8 100644
--- a/lib/ace/test/mockrenderer.js
+++ b/lib/ace/test/mockrenderer.js
@@ -126,6 +126,9 @@ MockRenderer.prototype.addMarker = function() {
 MockRenderer.prototype.setBreakpoints = function() {
 };
 
+MockRenderer.prototype.onResize = function() {
+};
+
 MockRenderer.prototype.updateFull = function() {
 };