diff --git a/src/Monolog/Handler/MandrillHandler.php b/src/Monolog/Handler/MandrillHandler.php
index 68ec5682..066c649e 100644
--- a/src/Monolog/Handler/MandrillHandler.php
+++ b/src/Monolog/Handler/MandrillHandler.php
@@ -46,7 +46,7 @@ class MandrillHandler extends MailHandler
     /**
      * {@inheritdoc}
      */
-    protected function send($content, array $records)
+    protected function send(string $content, array $records)
     {
         $mime = null;
         if ($this->isHtmlBody($content)) {
diff --git a/src/Monolog/Handler/SendGridHandler.php b/src/Monolog/Handler/SendGridHandler.php
index 3a91cb41..7d82d946 100644
--- a/src/Monolog/Handler/SendGridHandler.php
+++ b/src/Monolog/Handler/SendGridHandler.php
@@ -72,7 +72,7 @@ class SendGridHandler extends MailHandler
     /**
      * {@inheritdoc}
      */
-    protected function send($content, array $records)
+    protected function send(string $content, array $records)
     {
         $message = [];
         $message['api_user'] = $this->apiUser;