diff --git a/src/Data/NotOKException.php b/src/Data/NotOKException.php
index bc37359dfebb..ce68dc6e0aba 100644
--- a/src/Data/NotOKException.php
+++ b/src/Data/NotOKException.php
@@ -6,5 +6,5 @@
 /**
  * Signals that a result contains no value.
  */
-class NotOKException {
+class NotOKException extends Exception{
 }
diff --git a/src/Data/README.md b/src/Data/README.md
index f4651bf8e48a..3dfa3e4e71f4 100644
--- a/src/Data/README.md
+++ b/src/Data/README.md
@@ -35,7 +35,7 @@ assert(!$pi->isError());
 
 // Do some transformation with the value.
 $r = 10;
-$A = $f->map(function($value_of_pi) use ($r) { return 2 * $value_of_pi * $r; });
+$A = $pi->map(function($value_of_pi) use ($r) { return 2 * $value_of_pi * $r; });
 
 // Still ok and no error.
 assert($A->isOk());
diff --git a/src/Data/Result.php b/src/Data/Result.php
index b9a60e03a04b..21a487d59f0b 100644
--- a/src/Data/Result.php
+++ b/src/Data/Result.php
@@ -61,7 +61,7 @@ public function map(callable $f);
 	/**
 	 * Get a new result from the callable or do nothing if this is an error.
 	 *
-	 * If null is returned the result is not touched.
+	 * If null is returned from $f, the result is not touched.
 	 *
 	 * Does nothing if !isOK. This is monadic bind.
 	 *
@@ -74,7 +74,7 @@ public function then(callable $f);
 	 * Feed the error into a callable and replace this with the result
 	 * or do nothing if this is a value.
 	 *
-	 * If null is returned, the error in the result is not touched.
+	 * If null is returned from $f, the error in the result is not touched.
 	 *
 	 * Does nothing if !isError.
 	 *