diff --git a/framework/http/HeaderCollection.php b/framework/http/HeaderCollection.php
index 24fa572..a9c9d80 100644
--- a/framework/http/HeaderCollection.php
+++ b/framework/http/HeaderCollection.php
@@ -183,8 +183,12 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
     {
         $this->removeAll();
         foreach ($array as $name => $values) {
-            foreach ($values as $value) {
-                $this->add($name, $value);
+            if (is_array($values)) {
+                foreach ($values as $value) {
+                    $this->add($name, $value);
+                }
+            } else {
+                $this->add($name, $values);
             }
         }
     }
diff --git a/framework/web/Request.php b/framework/web/Request.php
index 416540b..e4a193b 100644
--- a/framework/web/Request.php
+++ b/framework/web/Request.php
@@ -236,10 +236,6 @@ class Request extends \yii\base\Request implements RequestInterface
             }
         }
 
-        foreach ($headers as $name => $value) {
-            $headers[strtolower($name)] = (array)$value;
-        }
-
         return $headers;
     }
 
diff --git a/tests/framework/filters/HostControlTest.php b/tests/framework/filters/HostControlTest.php
index 0cb1bc8..2da4104 100644
--- a/tests/framework/filters/HostControlTest.php
+++ b/tests/framework/filters/HostControlTest.php
@@ -91,7 +91,7 @@ class HostControlTest extends TestCase
      */
     public function testFilter($allowedHosts, $host, $allowed)
     {
-        $_SERVER['HTTP_HOST'] = $host;
+        Yii::$app->request->setHeader('Host', $host);
 
         $filter = new HostControl();
         $filter->allowedHosts = $allowedHosts;