diff --git a/src/Monolog/Handler/SlackHandler.php b/src/Monolog/Handler/SlackHandler.php
index bf279bbe..31e084c8 100644
--- a/src/Monolog/Handler/SlackHandler.php
+++ b/src/Monolog/Handler/SlackHandler.php
@@ -192,7 +192,7 @@ class SlackHandler extends SocketHandler
         return $this;
     }
 
-    public function getFormatter()
+    public function getFormatter(): FormatterInterface
     {
         $formatter = parent::getFormatter();
         $this->slackRecord->setFormatter($formatter);
diff --git a/src/Monolog/Handler/SlackWebhookHandler.php b/src/Monolog/Handler/SlackWebhookHandler.php
index 6ad3e45c..d69c926e 100644
--- a/src/Monolog/Handler/SlackWebhookHandler.php
+++ b/src/Monolog/Handler/SlackWebhookHandler.php
@@ -98,7 +98,7 @@ class SlackWebhookHandler extends AbstractProcessingHandler
         return $this;
     }
 
-    public function getFormatter()
+    public function getFormatter(): FormatterInterface
     {
         $formatter = parent::getFormatter();
         $this->slackRecord->setFormatter($formatter);