diff --git a/src/Russian/GeneralDeclension.php b/src/Russian/GeneralDeclension.php
index 8d3a374..7885553 100644
--- a/src/Russian/GeneralDeclension.php
+++ b/src/Russian/GeneralDeclension.php
@@ -55,6 +55,7 @@ class GeneralDeclension extends \morphos\GeneralDeclension implements Cases {
 
 	static protected $immutableWords = array(
 		'евро',
+		'пенни',
 	);
 
 	public function hasForms($word, $animateness = false) {
diff --git a/src/Russian/Plurality.php b/src/Russian/Plurality.php
index df3dd4f..fe0900e 100644
--- a/src/Russian/Plurality.php
+++ b/src/Russian/Plurality.php
@@ -18,6 +18,7 @@ class Plurality extends \morphos\Plurality implements Cases {
 
 	static protected $immutableWords = array(
 		'евро',
+		'пенни',
 	);
 
 	static public function pluralize($word, $count, $animateness = false) {