diff --git a/src/EasySms.php b/src/EasySms.php
index 7dcd4c9..9b4809e 100644
--- a/src/EasySms.php
+++ b/src/EasySms.php
@@ -261,6 +261,10 @@ protected function makeGateway($gateway, $config)
      */
     protected function formatGatewayClassName($name)
     {
+        if (\class_exists($name) && \in_array(GatewayInterface::class, \class_implements($name))) {
+            return $name;
+        }
+
         $name = \ucfirst(\str_replace(['-', '_', ''], '', $name));
 
         return __NAMESPACE__."\\Gateways\\{$name}Gateway";
diff --git a/tests/EasySmsTest.php b/tests/EasySmsTest.php
index d2c18fc..768de79 100644
--- a/tests/EasySmsTest.php
+++ b/tests/EasySmsTest.php
@@ -66,7 +66,7 @@ public function testGatewayWithDefaultSetting()
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage(
             sprintf(
-                'Class "%s" is a invalid easy-sms gateway.',
+                'Class "Overtrue\EasySms\Gateways\%sGateway" is a invalid easy-sms gateway.',
                 DummyInvalidGatewayForTest::class
             )
         );