diff --git a/src/Bartlett/Reflect/PhpParser/NodeProcessor.php b/src/Bartlett/Reflect/PhpParser/NodeProcessor.php
index <HASH>..<HASH> 100644
--- a/src/Bartlett/Reflect/PhpParser/NodeProcessor.php
+++ b/src/Bartlett/Reflect/PhpParser/NodeProcessor.php
@@ -33,7 +33,7 @@ interface NodeProcessor
      *
      * @return void
      */
-    public function push($callback);
+    public function push(callable $callback);
 
     /**
      * Gets list of processors that will check pre-conditions.
diff --git a/src/Bartlett/Reflect/PhpParser/NodeProcessorAbstract.php b/src/Bartlett/Reflect/PhpParser/NodeProcessorAbstract.php
index <HASH>..<HASH> 100644
--- a/src/Bartlett/Reflect/PhpParser/NodeProcessorAbstract.php
+++ b/src/Bartlett/Reflect/PhpParser/NodeProcessorAbstract.php
@@ -33,11 +33,9 @@ class NodeProcessorAbstract implements NodeProcessor
     /**
      * {@inheritdoc}
      */
-    public function push($callback)
+    public function push(callable $callback)
     {
-        if (is_callable($callback)) {
-            array_push($this->processors, $callback);
-        }
+        array_push($this->processors, $callback);
     }
 
     /**
Force TypeHint constraint and simplify code