diff --git a/lib/matchers/SubstringMatcher.js b/lib/matchers/SubstringMatcher.js
index <HASH>..<HASH> 100644
--- a/lib/matchers/SubstringMatcher.js
+++ b/lib/matchers/SubstringMatcher.js
@@ -1,14 +1,11 @@
 'use strict';
 
 var _ = require('lodash-node')
-	, TypeSafeMatcher = require('./TypeSafeMatcher')
+	, IsString = require('./IsString')
 	;
 
 function SubstringMatcher(substring, relation, matchesString) {
-	return _.create(new TypeSafeMatcher(), {
-		isExpectedType: function (actual) {
-			return _.isString(actual);
-		},
+	return _.create(new IsString(), {
 		matchesSafely: function (actual) {
 			return matchesString.call(this, actual);
 		},
Reimplement SubstringMatcher as child of IsString