diff --git a/src/OAuth1/AbstractProvider.php b/src/OAuth1/AbstractProvider.php
index 5c1add1..9ba50df 100644
--- a/src/OAuth1/AbstractProvider.php
+++ b/src/OAuth1/AbstractProvider.php
@@ -3,6 +3,7 @@
 namespace SocialiteProviders\Manager\OAuth1;
 
 use Illuminate\Http\RedirectResponse;
+use InvalidArgumentException;
 use Laravel\Socialite\One\AbstractProvider as BaseProvider;
 use League\OAuth1\Client\Credentials\TokenCredentials;
 use SocialiteProviders\Manager\ConfigTrait;
@@ -42,7 +43,7 @@ public static function serviceContainerKey($providerName)
     public function user()
     {
         if (!$this->hasNecessaryVerifier()) {
-            throw new \InvalidArgumentException('Invalid request. Missing OAuth verifier.');
+            throw new InvalidArgumentException('Invalid request. Missing OAuth verifier.');
         }
 
         $token = $this->getToken();
diff --git a/src/OAuth1/Server.php b/src/OAuth1/Server.php
index 587289b..73cf2c8 100644
--- a/src/OAuth1/Server.php
+++ b/src/OAuth1/Server.php
@@ -2,7 +2,9 @@
 
 namespace SocialiteProviders\Manager\OAuth1;
 
+use GuzzleHttp\Client;
 use GuzzleHttp\Exception\BadResponseException;
+use InvalidArgumentException;
 use League\OAuth1\Client\Credentials\TemporaryCredentials;
 use League\OAuth1\Client\Server\Server as BaseServer;
 use SocialiteProviders\Manager\ConfigTrait;
@@ -46,7 +48,7 @@ abstract class Server extends BaseServer
     public function getTokenCredentials(TemporaryCredentials $temporaryCredentials, $temporaryIdentifier, $verifier)
     {
         if ($temporaryIdentifier !== $temporaryCredentials->getIdentifier()) {
-            throw new \InvalidArgumentException(
+            throw new InvalidArgumentException(
                 'Temporary identifier passed back by server does not match that of stored temporary credentials.
                 Potential man-in-the-middle.'
             );
@@ -60,7 +62,7 @@ public function getTokenCredentials(TemporaryCredentials $temporaryCredentials,
         $headers = $this->getHeaders($temporaryCredentials, 'POST', $uri, $bodyParameters);
 
         try {
-            if ('GuzzleHttp\\Client' === get_class($client)) {
+            if ($client instanceof Client) {
                 $response = $client->post($uri, [
                     'headers'     => $headers,
                     'form_params' => $bodyParameters,