diff --git a/src/Pinyin/Pinyin.php b/src/Pinyin/Pinyin.php
index 71bdb4c4..a21ecf48 100644
--- a/src/Pinyin/Pinyin.php
+++ b/src/Pinyin/Pinyin.php
@@ -152,7 +152,7 @@ public static function pinyin($string, array $settings = array())
      *
      * @return string
      */
-    public static function letter($string, $setting = array())
+    public static function letter($string, array $setting = array())
     {
         $default = array('delimiter' => null, 'uppercase' => false);
         $setting = array_merge($default, $setting);
diff --git a/tests/TestCase.php b/tests/TestCase.php
index f6e87e3e..4062c9f0 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -38,8 +38,8 @@ public function testLetters()
         $this->assertEquals('N-H', Pinyin::letter('您好', array('delimiter' => '-', 'uppercase' => true)));
         $this->assertEquals('c q', Pinyin::letter('重庆'));
         $this->assertEquals('z y', Pinyin::letter('重要'));
-        $this->assertEquals('nh', Pinyin::letter('您好', ''));
-        $this->assertEquals('kxll', Pinyin::letter('康熙来了', ''));
+        $this->assertEquals('nh', Pinyin::letter('您好', array('delimiter' => '')));
+        $this->assertEquals('kxll', Pinyin::letter('康熙来了', array('delimiter' => '')));
         $this->assertEquals('d z x w q l x b d d z d g m h', Pinyin::letter('带着希望去旅行，比到达终点更美好'));
         $this->assertEquals('z q s l z w z w', Pinyin::letter('赵钱孙李 周吴郑王'));
     }