diff --git a/src/Monolog/Handler/DeduplicationHandler.php b/src/Monolog/Handler/DeduplicationHandler.php
index 7881cc4e..96b29e15 100644
--- a/src/Monolog/Handler/DeduplicationHandler.php
+++ b/src/Monolog/Handler/DeduplicationHandler.php
@@ -67,7 +67,7 @@ class DeduplicationHandler extends BufferHandler
         parent::__construct($handler, 0, Logger::DEBUG, $bubble, false);
 
         $this->deduplicationStore = $deduplicationStore === null ? sys_get_temp_dir() . '/monolog-dedup-' . substr(md5(__FILE__), 0, 20) .'.log' : $deduplicationStore;
-        $this->deduplicationLevel = $deduplicationLevel;
+        $this->deduplicationLevel = Logger::toMonologLevel($deduplicationLevel);
         $this->time = $time;
     }