diff --git a/Message/Console/Header.php b/Message/Console/Header.php
index 569f9d7a7..7bde08cfa 100644
--- a/Message/Console/Header.php
+++ b/Message/Console/Header.php
@@ -69,7 +69,7 @@ final class Header extends HeaderAbstract
      */
     public function set(string $key, string $header, bool $overwrite = false) : bool
     {
-        if (self::$isLocked) {
+        if ($this->isLocked) {
             return false;
         }
 
@@ -109,7 +109,7 @@ final class Header extends HeaderAbstract
      */
     public function remove($key) : bool
     {
-        if (self::$isLocked) {
+        if ($this->isLocked) {
             return false;
         }
 
diff --git a/tests/Message/Console/HeaderTest.php b/tests/Message/Console/HeaderTest.php
index 298223aeb..1d8045b6f 100644
--- a/tests/Message/Console/HeaderTest.php
+++ b/tests/Message/Console/HeaderTest.php
@@ -59,20 +59,16 @@ class HeaderTest extends \PHPUnit\Framework\TestCase
     public function testLockedHeaderSet()
     {
         $header = new Header();
-        Header::lock();
-        self::assertTrue(Header::isLocked());
+        $header->lock();
+        self::assertTrue($header->isLocked());
         self::assertFalse($header->set('key', 'value'));
-
-        TestUtils::setMember('phpOMS\Message\Console\Header', 'isLocked', false);
     }
 
     public function testLockedHeaderRemove()
     {
         $header = new Header();
-        Header::lock();
-        self::assertTrue(Header::isLocked());
+        $header->lock();
+        self::assertTrue($header->isLocked());
         self::assertFalse($header->remove('key'));
-
-        TestUtils::setMember('phpOMS\Message\Console\Header', 'isLocked', false);
     }
 }
diff --git a/tests/Message/Http/HeaderTest.php b/tests/Message/Http/HeaderTest.php
index 46121fc91..ad99151b1 100644
--- a/tests/Message/Http/HeaderTest.php
+++ b/tests/Message/Http/HeaderTest.php
@@ -41,7 +41,6 @@ class HeaderTest extends \PHPUnit\Framework\TestCase
         self::assertTrue(Header::isSecurityHeader('X-xss-protection'));
         self::assertTrue(Header::isSecurityHeader('x-conTent-tYpe-options'));
         self::assertTrue(Header::isSecurityHeader('x-frame-options'));
-
         self::assertFalse(Header::isSecurityHeader('x-frame-optionss'));
     }
 
@@ -73,8 +72,6 @@ class HeaderTest extends \PHPUnit\Framework\TestCase
         $header->lock();
         self::assertTrue($header->isLocked());
         self::assertFalse($header->set('key', 'value'));
-
-        TestUtils::setMember('phpOMS\Message\Http\Header', 'isLocked', false);
     }
 
     public function testLockedHeaderRemove()
@@ -83,8 +80,6 @@ class HeaderTest extends \PHPUnit\Framework\TestCase
         $header->lock();
         self::assertTrue($header->isLocked());
         self::assertFalse($header->remove('key'));
-
-        TestUtils::setMember('phpOMS\Message\Http\Header', 'isLocked', false);
     }
 
     public function testGeneration()