diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index af1bfa0..1290304 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -83,6 +83,7 @@ private function createClientsNode()
 
                     // @todo @deprecated
                     ->arrayNode('headers')
+                        ->normalizeKeys(false)
                         ->prototype('scalar')
                         ->end()
                     ->end()
@@ -90,6 +91,7 @@ private function createClientsNode()
                     ->arrayNode('options')
                         ->children()
                             ->arrayNode('headers')
+                                ->normalizeKeys(false)
                                 ->prototype('scalar')
                                 ->end()
                             ->end()
diff --git a/DependencyInjection/GuzzleExtension.php b/DependencyInjection/GuzzleExtension.php
index 66a07f4..17aff21 100644
--- a/DependencyInjection/GuzzleExtension.php
+++ b/DependencyInjection/GuzzleExtension.php
@@ -53,12 +53,6 @@ public function load(array $configs, ContainerBuilder $container)
                 'handler'  => $this->createHandler($container, $name, $options)
             ];
 
-            // header hotfix/workaround #77
-            // @todo @deprecated
-            if (isset($options['headers'])) {
-                $argument['headers'] = $this->cleanUpHeaders($options['headers']);
-            }
-
             // if present, add default options to the constructor argument for the Guzzle client
             if (array_key_exists('options', $options) && is_array($options['options'])) {
 
@@ -68,12 +62,6 @@ public function load(array $configs, ContainerBuilder $container)
                         continue;
                     }
 
-                    // @todo: cleanup
-                    if ($key === 'headers') {
-                        $argument[$key] = $this->cleanUpHeaders($value);
-                        continue;
-                    }
-
                     $argument[$key] = $value;
                 }
             }
@@ -235,31 +223,6 @@ protected function createWsseMiddleware($username, $password, $createdAtExpressi
         return $wsse;
     }
 
-    /**
-     * Clean up HTTP headers
-     *
-     * @since  2015-07
-     *
-     * @param  array $headers
-     *
-     * @return array
-     */
-    protected function cleanUpHeaders(array $headers)
-    {
-        foreach ($headers as $name => $value) {
-
-            // because of standard conventions in YAML dashes are converted to underscores
-            // underscores are not allowed in HTTP standard, will be replaced by dash
-            $nameClean = str_replace('_', '-', $name);
-
-            unset($headers[$name]);
-
-            $headers[$nameClean] = $value;
-        }
-
-        return $headers;
-    }
-
     /**
      * Returns alias of extension
      *
diff --git a/Tests/DependencyInjection/ConfigurationTest.php b/Tests/DependencyInjection/ConfigurationTest.php
index b028a5d..0f8b834 100644
--- a/Tests/DependencyInjection/ConfigurationTest.php
+++ b/Tests/DependencyInjection/ConfigurationTest.php
@@ -196,4 +196,38 @@ public function testSingleClientConfigWithProxyAsString()
             'clients' => ['test_client' => ['options' => ['proxy' => ['http' => 'http://proxy.org']]]]
         ]), $processedConfig);
     }
+
+    public function testHeaderWithUnderscore()
+    {
+        $config = [
+            'guzzle' => [
+                'clients' => [
+                    'test_client' => [
+                        'headers' => [
+                            'Header_underscored' => 'some-random-hash',
+                            'Header-hyphened' => 'another-random-hash'
+                        ],
+                        'options' => [
+                            'headers' => [
+                                'Header_underscored' => 'some-random-hash',
+                                'Header-hyphened' => 'another-random-hash'
+                            ],
+                        ]
+                    ]
+                ]
+            ]
+        ];
+
+        $processor = new Processor();
+        $processedConfig = $processor->processConfiguration(new Configuration(true), $config);
+
+        $headers = $processedConfig['clients']['test_client']['headers'];
+        $optionsHeaders = $processedConfig['clients']['test_client']['options']['headers'];
+
+        foreach ([$headers, $optionsHeaders] as $headerConfig)
+        {
+            $this->assertArrayHasKey('Header_underscored', $headerConfig);
+            $this->assertArrayHasKey('Header-hyphened', $headerConfig);
+        }
+    }
 }