diff --git a/src/Headers.php b/src/Headers.php
index 585be8b..786f4cb 100644
--- a/src/Headers.php
+++ b/src/Headers.php
@@ -37,7 +37,7 @@ public function __construct(array $headers = [], ?array $globals = null)
     /**
      * {@inheritdoc}
      */
-    public function addHeader(string $name, $value): HeadersInterface
+    public function addHeader($name, $value): HeadersInterface
     {
         [$values, $originalName, $normalizedName] = $this->prepareHeader($name, $value);
 
@@ -84,7 +84,7 @@ public function getHeader(string $name, $default = []): array
     /**
      * {@inheritdoc}
      */
-    public function setHeader(string $name, $value): HeadersInterface
+    public function setHeader($name, $value): HeadersInterface
     {
         [$values, $originalName, $normalizedName] = $this->prepareHeader($name, $value);
 
@@ -202,7 +202,7 @@ protected function trimHeaderValue($value): array
      *
      * @return array
      */
-    protected function prepareHeader(string $name, $value): array
+    protected function prepareHeader($name, $value): array
     {
         $this->validateHeader($name, $value);
         $values = $this->trimHeaderValue($value);
@@ -234,10 +234,10 @@ protected function prepareHeader(string $name, $value): array
      *
      * @throws InvalidArgumentException;
      */
-    protected function validateHeader(string $name, $value)
+    protected function validateHeader($name, $value)
     {
-        self::validateHeaderName($name);
-        self::validateHeaderValue($value);
+        $this->validateHeaderName($name);
+        $this->validateHeaderValue($value);
     }
 
     /**
@@ -245,7 +245,7 @@ protected function validateHeader(string $name, $value)
      *
      * @throws InvalidArgumentException
      */
-    public static function validateHeaderName($name)
+    protected function validateHeaderName($name)
     {
         if (!is_string($name) || preg_match("@^[!#$%&'*+.^_`|~0-9A-Za-z-]+$@", $name) !== 1) {
             throw new InvalidArgumentException('Header name must be an RFC 7230 compatible string.');
@@ -257,7 +257,7 @@ public static function validateHeaderName($name)
      *
      * @throws InvalidArgumentException
      */
-    public static function validateHeaderValue($value)
+    protected function validateHeaderValue($value)
     {
         $items = is_array($value) ? $value : [$value];
 
diff --git a/src/Interfaces/HeadersInterface.php b/src/Interfaces/HeadersInterface.php
index 80bc76a..4a6eecc 100644
--- a/src/Interfaces/HeadersInterface.php
+++ b/src/Interfaces/HeadersInterface.php
@@ -25,7 +25,7 @@ interface HeadersInterface
      *
      * @throws InvalidArgumentException
      */
-    public function addHeader(string $name, $value): HeadersInterface;
+    public function addHeader($name, $value): HeadersInterface;
 
     /**
      * Remove header value
@@ -57,7 +57,7 @@ public function getHeader(string $name, $default = []): array;
      *
      * @throws InvalidArgumentException
      */
-    public function setHeader(string $name, $value): HeadersInterface;
+    public function setHeader($name, $value): HeadersInterface;
 
     /**
      * Replaces all existing headers with the new values.
diff --git a/src/Message.php b/src/Message.php
index 112c40a..edf35f8 100644
--- a/src/Message.php
+++ b/src/Message.php
@@ -118,9 +118,6 @@ public function getHeaderLine($name): string
      */
     public function withHeader($name, $value)
     {
-        Headers::validateHeaderName($name);
-        Headers::validateHeaderValue($value);
-
         $clone = clone $this;
         $clone->headers->setHeader($name, $value);
 
@@ -136,9 +133,6 @@ public function withHeader($name, $value)
      */
     public function withAddedHeader($name, $value)
     {
-        Headers::validateHeaderName($name);
-        Headers::validateHeaderValue($value);
-
         $clone = clone $this;
         $clone->headers->addHeader($name, $value);