diff --git a/lib/suite.js b/lib/suite.js
index b693ce10c4..191d946b50 100644
--- a/lib/suite.js
+++ b/lib/suite.js
@@ -493,16 +493,6 @@ Suite.prototype.appendOnlySuite = function(suite) {
   this._onlySuites.push(suite);
 };
 
-/**
- * Marks a suite to be `only`.
- *
- * @private
- * @param {Suite} suite
- */
-Suite.prototype.markOnly = function() {
-  this.parent.appendOnlySuite(this);
-};
-
 /**
  * Adds a test to the list of tests marked `only`.
  *