diff --git a/src/JsonSchema/Constraints/String.php b/src/JsonSchema/Constraints/String.php
index 7bc3eb83..246c06b4 100644
--- a/src/JsonSchema/Constraints/String.php
+++ b/src/JsonSchema/Constraints/String.php
@@ -23,12 +23,12 @@ class String extends Constraint
     public function check($element, $schema = null, $path = null, $i = null)
     {
         // Verify maxLength
-        if (isset($schema->maxLength) && strlen($element) > $schema->maxLength) {
+        if (isset($schema->maxLength) && $this->strlen($element) > $schema->maxLength) {
             $this->addError($path, "must be at most " . $schema->maxLength . " characters long");
         }
 
         //verify minLength
-        if (isset($schema->minLength) && strlen($element) < $schema->minLength) {
+        if (isset($schema->minLength) && $this->strlen($element) < $schema->minLength) {
             $this->addError($path, "must be at least " . $schema->minLength . " characters long");
         }
 
@@ -39,4 +39,13 @@ public function check($element, $schema = null, $path = null, $i = null)
 
         $this->checkFormat($element, $schema, $path, $i);
     }
+
+    private function strlen($string)
+    {
+        if (extension_loaded('mbstring')) {
+            return mb_strlen($string, mb_detect_encoding($string));
+        } else {
+            return strlen($string);
+        }
+    }
 }
diff --git a/tests/JsonSchema/Tests/Constraints/MinLengthMaxLengthMultiByteTest.php b/tests/JsonSchema/Tests/Constraints/MinLengthMaxLengthMultiByteTest.php
new file mode 100644
index 00000000..df00ce42
--- /dev/null
+++ b/tests/JsonSchema/Tests/Constraints/MinLengthMaxLengthMultiByteTest.php
@@ -0,0 +1,76 @@
+<?php
+
+/*
+ * This file is part of the JsonSchema package.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace JsonSchema\Tests\Constraints;
+
+class MinLengthMaxLengthMultiByteTest extends BaseTestCase
+{
+    protected function setUp()
+    {
+        if (! extension_loaded('mbstring')) {
+            $this->markTestSkipped('mbstring extension is not available');
+        }
+    }
+
+    public function getInvalidTests()
+    {
+        return array(
+            array(
+                '{
+                  "value":"☀"
+                }',
+                '{
+                  "type":"object",
+                  "properties":{
+                    "value":{"type":"string","minLength":2,"maxLength":4}
+                  }
+                }'
+            ),
+            array(
+                '{
+                  "value":"☀☁☂☃☺"
+                }',
+                '{
+                  "type":"object",
+                  "properties":{
+                    "value":{"type":"string","minLength":2,"maxLength":4}
+                  }
+                }'
+            )
+        );
+    }
+
+    public function getValidTests()
+    {
+        return array(
+            array(
+                '{
+                  "value":"☀☁"
+                }',
+                '{
+                  "type":"object",
+                  "properties":{
+                    "value":{"type":"string","minLength":2,"maxLength":4}
+                  }
+                }'
+            ),
+            array(
+                '{
+                  "value":"☀☁☂☃"
+                }',
+                '{
+                  "type":"object",
+                  "properties":{
+                    "value":{"type":"string","minLength":2,"maxLength":4}
+                  }
+                }'
+            )
+        );
+    }
+}