diff --git a/src/Monolog/Formatter/LineFormatter.php b/src/Monolog/Formatter/LineFormatter.php
index a96fb27d..53269c78 100644
--- a/src/Monolog/Formatter/LineFormatter.php
+++ b/src/Monolog/Formatter/LineFormatter.php
@@ -94,7 +94,7 @@ class LineFormatter extends NormalizerFormatter
 
         $data = $this->normalize($data);
         if (version_compare(PHP_VERSION, '5.4.0', '>=')) {
-            return $this->toJson($data);
+            return $this->toJson($data, true);
         }
 
         return str_replace('\\/', '/', json_encode($data));