diff --git a/src/LoaderInterface.php b/src/LoaderInterface.php
index fe50932..9a4f969 100644
--- a/src/LoaderInterface.php
+++ b/src/LoaderInterface.php
@@ -15,7 +15,7 @@ interface LoaderInterface
     /**
      * Loads data in the given sink.
      *
-     * @return \Generator<mixed, ResultBucketInterface<OutputType>, InputType, void>
+     * @return \Generator<positive-int, ResultBucketInterface<OutputType>, InputType|null, void>
      */
     public function load(): \Generator;
 }
diff --git a/src/PipelineRunnerInterface.php b/src/PipelineRunnerInterface.php
index a3d87c4..aed94e0 100644
--- a/src/PipelineRunnerInterface.php
+++ b/src/PipelineRunnerInterface.php
@@ -13,7 +13,7 @@ interface PipelineRunnerInterface
      * @template OutputType of non-empty-array<array-key, mixed>|object
      *
      * @param \Iterator<positive-int, InputType|null> $source
-     * @param \Generator<positive-int, ResultBucketInterface<InputType>, InputType, void> $coroutine
+     * @param \Generator<positive-int, ResultBucketInterface<InputType>, InputType|null, void> $coroutine
      * @param StepRejectionInterface<InputType> $rejection
      * @param StepStateInterface $state
      * @return \Iterator<positive-int, ResultBucketInterface<OutputType>|null>
diff --git a/src/TransformerInterface.php b/src/TransformerInterface.php
index 18d731a..dea18c2 100644
--- a/src/TransformerInterface.php
+++ b/src/TransformerInterface.php
@@ -15,7 +15,7 @@ interface TransformerInterface
     /**
      * Transforms the data from one format to another.
      *
-     * @return \Generator<mixed, ResultBucketInterface<OutputType>, InputType, void>
+     * @return \Generator<positive-int, ResultBucketInterface<OutputType>, InputType|null, void>
      */
     public function transform(): \Generator;
 }