diff --git a/src/Composer/Installer/InstallationManager.php b/src/Composer/Installer/InstallationManager.php
index 3aa4be7c6..55e1eef4b 100644
--- a/src/Composer/Installer/InstallationManager.php
+++ b/src/Composer/Installer/InstallationManager.php
@@ -245,7 +245,7 @@ class InstallationManager
                     $opts = array('http' =>
                         array(
                             'method'  => 'POST',
-                            'header'  => 'Content-type: application/x-www-form-urlencoded',
+                            'header'  => array('Content-type: application/x-www-form-urlencoded'),
                             'content' => http_build_query($params, '', '&'),
                             'timeout' => 3,
                         )
@@ -269,7 +269,7 @@ class InstallationManager
             $opts = array('http' =>
                 array(
                     'method'  => 'POST',
-                    'header'  => 'Content-Type: application/json',
+                    'header'  => array('Content-Type: application/json'),
                     'content' => json_encode($postData),
                     'timeout' => 6,
                 )
diff --git a/src/Composer/Util/StreamContextFactory.php b/src/Composer/Util/StreamContextFactory.php
index 590bed581..5c335ce9c 100644
--- a/src/Composer/Util/StreamContextFactory.php
+++ b/src/Composer/Util/StreamContextFactory.php
@@ -67,19 +67,12 @@ final class StreamContextFactory
                     $auth .= ':' . $proxy['pass'];
                 }
                 $auth = base64_encode($auth);
-                $authHeader = "Proxy-Authorization: Basic {$auth}";
 
                 // Preserve headers if already set in default options
                 if (isset($defaultOptions['http']['header'])) {
-                     if (is_array($defaultOptions['http']['header']))
-                        $defaultOptions['http']['header'][] = $authHeader;
-                    else
-                        $defaultOptions['http']['header'] = array(
-                            $defaultOptions['http']['header'],
-                            $authHeader
-                        );
+                    $defaultOptions['http']['header'][] = "Proxy-Authorization: Basic {$auth}";
                 } else {
-                    $options['http']['header'] = array($authHeader);
+                    $options['http']['header'] = array("Proxy-Authorization: Basic {$auth}");
                 }
             }
         }
diff --git a/tests/Composer/Test/Util/StreamContextFactoryTest.php b/tests/Composer/Test/Util/StreamContextFactoryTest.php
index 5d7969660..3d728ffeb 100644
--- a/tests/Composer/Test/Util/StreamContextFactoryTest.php
+++ b/tests/Composer/Test/Util/StreamContextFactoryTest.php
@@ -126,20 +126,6 @@ class StreamContextFactoryTest extends \PHPUnit_Framework_TestCase
         }
     }
 
-    public function testHttpProxyWithContentTypeHeader() {
-         $_SERVER['http_proxy'] = 'http://username:password@proxyserver.net';
-
-        $context = StreamContextFactory::getContext(array('http' => array('method' => 'GET', 'header' => 'Content-Type: application/json')));
-        $options = stream_context_get_options($context);
-
-        $this->assertEquals(array('http' => array(
-            'proxy' => 'tcp://proxyserver.net:80',
-            'request_fulluri' => true,
-            'method' => 'GET',
-            'header' => array("Content-Type: application/json", "Proxy-Authorization: Basic " . base64_encode('username:password'))
-        )), $options);
-    }
-
     public function dataSSLProxy()
     {
         return array(