diff --git a/src/Gateways/ErrorlogGateway.php b/src/Gateways/ErrorlogGateway.php
index 80d2191..b605cf6 100644
--- a/src/Gateways/ErrorlogGateway.php
+++ b/src/Gateways/ErrorlogGateway.php
@@ -27,7 +27,7 @@ class ErrorlogGateway extends Gateway
     public function send($to, MessageInterface $message, Config $config)
     {
         if (is_array($to)) {
-            $to = join(',', $to);
+            $to = implode(',', $to);
         }
 
         $message = sprintf(
diff --git a/src/Gateways/SendcloudGateway.php b/src/Gateways/SendcloudGateway.php
index 84e662c..6d9f5b3 100644
--- a/src/Gateways/SendcloudGateway.php
+++ b/src/Gateways/SendcloudGateway.php
@@ -41,7 +41,7 @@ public function send($to, MessageInterface $message, Config $config)
         $params = [
             'smsUser' => $config->get('sms_user'),
             'templateId' => $message->getTemplate(),
-            'phone' => is_array($to) ? join(',', $to) : $to,
+            'phone' => is_array($to) ? implode(',', $to) : $to,
             'vars' => $this->formatTemplateVars($message->getData()),
             'timestamp' => time(),
         ];
diff --git a/src/Messenger.php b/src/Messenger.php
index e11edc8..be5fc7c 100644
--- a/src/Messenger.php
+++ b/src/Messenger.php
@@ -112,7 +112,7 @@ protected function formatGateways(array $gateways)
         $config = $this->easySms->getConfig();
 
         foreach ($gateways as $gateway => $setting) {
-            if (is_integer($gateway) && is_string($setting)) {
+            if (is_int($gateway) && is_string($setting)) {
                 $gateway = $setting;
                 $setting = [];
             }
diff --git a/tests/Gateways/SendcloudGatewayTest.php b/tests/Gateways/SendcloudGatewayTest.php
index cd98b2d..2e39f45 100644
--- a/tests/Gateways/SendcloudGatewayTest.php
+++ b/tests/Gateways/SendcloudGatewayTest.php
@@ -39,7 +39,7 @@ public function testSend()
                 foreach ($expected as $key => $value) {
                     $signString[] = "{$key}={$value}";
                 }
-                $signString = join('&', $signString);
+                $signString = implode('&', $signString);
 
                 $expectedSignature = md5("{$config['sms_key']}&{$signString}&{$config['sms_key']}");