diff --git a/src/Processors/NullStringProcessor.php b/src/Processors/NullStringProcessor.php
index cd58cc3..51cd325 100644
--- a/src/Processors/NullStringProcessor.php
+++ b/src/Processors/NullStringProcessor.php
@@ -3,8 +3,9 @@
 namespace Hedii\LaravelGelfLogger\Processors;
 
 use Monolog\LogRecord;
+use Monolog\Processor\ProcessorInterface;
 
-class NullStringProcessor
+class NullStringProcessor implements ProcessorInterface
 {
     /**
      * Transform a "NULL" string record into a null value.
diff --git a/src/Processors/RenameIdFieldProcessor.php b/src/Processors/RenameIdFieldProcessor.php
index a9d421f..5e4b4f4 100644
--- a/src/Processors/RenameIdFieldProcessor.php
+++ b/src/Processors/RenameIdFieldProcessor.php
@@ -3,8 +3,9 @@
 namespace Hedii\LaravelGelfLogger\Processors;
 
 use Monolog\LogRecord;
+use Monolog\Processor\ProcessorInterface;
 
-class RenameIdFieldProcessor
+class RenameIdFieldProcessor implements ProcessorInterface
 {
     /**
      * Rename "id" field  to "_id" (additional field 'id' is not allowed).