diff --git a/src/Polygon.php b/src/Polygon.php
index b649b16..46ab1e3 100644
--- a/src/Polygon.php
+++ b/src/Polygon.php
@@ -128,12 +128,12 @@ public function offsetGet($offset)
 
     public function offsetUnset($offset)
     {
-        throw new \BadMethodCallException('Polyline is immutable.');
+        throw new \BadMethodCallException('Polygon is immutable.');
     }
 
     public function offsetSet($offset, $value)
     {
-        throw new \BadMethodCallException('Polyline is immutable.');
+        throw new \BadMethodCallException('Polygon is immutable.');
     }
 
     public function getIterator()