diff --git a/src/Pipeline/Interfaces/Pipeline.php b/src/Pipeline/Interfaces/Pipeline.php
index <HASH>..<HASH> 100644
--- a/src/Pipeline/Interfaces/Pipeline.php
+++ b/src/Pipeline/Interfaces/Pipeline.php
@@ -22,14 +22,14 @@ interface Pipeline extends \IteratorAggregate
     /**
      * @param callable $func
      *
-     * @return PipelineInterface
+     * @return Pipeline
      */
     public function map(callable $func);
 
     /**
      * @param callable $func - must yield values (return a generator)
      *
-     * @return PipelineInterface
+     * @return Pipeline
      */
     public function filter(callable $func);
 
diff --git a/src/Pipeline/Principal.php b/src/Pipeline/Principal.php
index <HASH>..<HASH> 100644
--- a/src/Pipeline/Principal.php
+++ b/src/Pipeline/Principal.php
@@ -34,7 +34,7 @@ abstract class Principal implements Interfaces\Pipeline
     /**
      * Optional source of data.
      *
-     * @param \Traversable $input
+     * @param \Traversable|null $input
      */
     public function __construct(\Traversable $input = null)
     {
Fixes for PHPDoc as spotted by Phan