diff --git a/src/Core/OAuth1Provider.php b/src/Core/OAuth1Provider.php
index 44c2cca..69a94ec 100644
--- a/src/Core/OAuth1Provider.php
+++ b/src/Core/OAuth1Provider.php
@@ -195,25 +195,58 @@ public function getAccessToken(string $requestToken, string $verifier):AccessTok
 			throw new ProviderException('request token mismatch');
 		}
 
-		$response = $this->sendAccessTokenRequest($verifier);
+		$params   = $this->getAccessTokenRequestHeaderParams($token, $verifier);
+		$response = $this->sendAccessTokenRequest($params);
 
 		return $this->parseTokenResponse($response);
 	}
 
+	/**
+	 * Prepares the header params for the access token request
+	 */
+	protected function getAccessTokenRequestHeaderParams(AccessToken $requestToken, string $verifier):array{
+
+		$params = [
+			'oauth_consumer_key'     => $this->options->key,
+			'oauth_nonce'            => $this->nonce(),
+			'oauth_signature_method' => 'HMAC-SHA1',
+			'oauth_timestamp'        => time(),
+			'oauth_token'            => $requestToken->accessToken,
+			'oauth_version'          => '1.0',
+			'oauth_verifier'         => $verifier,
+		];
+
+		$params['oauth_signature'] = $this->getSignature(
+			$this->accessTokenURL,
+			$params,
+			'POST',
+			$requestToken->accessTokenSecret,
+		);
+
+		return $params;
+	}
+
+	/**
+	 * Adds the "Authorization" header to the given `RequestInterface` using the given array or parameters
+	 */
+	protected function setAuthorizationHeader(RequestInterface $request, array $params):RequestInterface{
+		return $request->withHeader('Authorization', sprintf('OAuth %s', QueryUtil::build($params, null, ', ', '"')));
+	}
+
 	/**
 	 * Sends the access token request
 	 *
 	 * @see \chillerlan\OAuth\Core\OAuth1Provider::getAccessToken()
 	 */
-	protected function sendAccessTokenRequest(string $verifier):ResponseInterface{
+	protected function sendAccessTokenRequest(array $headerParams):ResponseInterface{
 
 		$request = $this->requestFactory
-			->createRequest('POST', QueryUtil::merge($this->accessTokenURL, ['oauth_verifier' => $verifier]))
+			->createRequest('POST', $this->accessTokenURL)
 			->withHeader('Accept-Encoding', 'identity')
 			->withHeader('Content-Length', '0')
 		;
 
-		$request = $this->getRequestAuthorization($request);
+		$request = $this->setAuthorizationHeader($request, $headerParams);
 
 		return $this->http->sendRequest($request);
 	}
@@ -245,7 +278,7 @@ public function getRequestAuthorization(RequestInterface $request, AccessToken|n
 			$token->accessTokenSecret,
 		);
 
-		return $request->withHeader('Authorization', sprintf('OAuth %s', QueryUtil::build($params, null, ', ', '"')));
+		return $this->setAuthorizationHeader($request, $params);
 	}
 
 }
diff --git a/tests/Providers/Unit/OAuth1ProviderUnitTestAbstract.php b/tests/Providers/Unit/OAuth1ProviderUnitTestAbstract.php
index 71934ce..adaf7e0 100644
--- a/tests/Providers/Unit/OAuth1ProviderUnitTestAbstract.php
+++ b/tests/Providers/Unit/OAuth1ProviderUnitTestAbstract.php
@@ -155,6 +155,30 @@ public function testParseTokenResponseConfirmCallbackException():void{
 	 * access token
 	 */
 
+	public function testGetAccessTokenRequestHeaderParams():void{
+
+		$testRequestToken = $this->getTestToken([
+			'accessToken'       => 'test_request_token',
+			'accessTokenSecret' => 'test_request_token_secret',
+		]);
+
+		$testVerifier = '*verifier*';
+
+		$headerParams = $this->invokeReflectionMethod('getAccessTokenRequestHeaderParams', [$testRequestToken, $testVerifier]);
+
+		$this::assertArrayHasKey('oauth_verifier', $headerParams);
+		$this::assertSame($testVerifier, $headerParams['oauth_verifier']);
+
+		$this::assertArrayHasKey('oauth_token', $headerParams);
+		$this::assertSame($testRequestToken->accessToken, $headerParams['oauth_token']);
+
+		$this::assertArrayHasKey('oauth_consumer_key', $headerParams);
+		$this::assertArrayHasKey('oauth_nonce', $headerParams);
+		$this::assertArrayHasKey('oauth_signature_method', $headerParams);
+		$this::assertArrayHasKey('oauth_timestamp', $headerParams);
+		$this::assertArrayHasKey('oauth_signature', $headerParams);
+	}
+
 	public function testGetAccessToken():void{
 		$this->setMockResponse($this->streamFactory->createStream($this::TEST_ACCESS_TOKEN));
 
@@ -179,16 +203,12 @@ public function testSendAccessTokenRequest():void{
 			'expires'           => AccessToken::NEVER_EXPIRES,
 		]);
 
-
 		$this->provider->storeAccessToken($requestToken);
 
-		$response = $this->invokeReflectionMethod('sendAccessTokenRequest', ['*verifier*']);
+		$response = $this->invokeReflectionMethod('sendAccessTokenRequest', [['foo' => 'bar']]);
 		$json     = MessageUtil::decodeJSON($response);
 
-		// check if the verifier is set
-		$this::assertSame('*verifier*', $json->request->params->{'oauth_verifier'});
-
-		$this::assertTrue(str_starts_with($json->headers->{'Authorization'}, 'OAuth '));
+		$this::assertSame('OAuth foo="bar"', $json->headers->{'Authorization'});
 		$this::assertSame('identity', $json->headers->{'Accept-Encoding'});
 		$this::assertSame('0', $json->headers->{'Content-Length'});
 		$this::assertSame('POST', $json->request->method);