diff --git a/Math/Optimization/Graph/Graph.php b/Math/Optimization/Graph/Graph.php
index 2a7412bc0..cb1db1aaa 100644
--- a/Math/Optimization/Graph/Graph.php
+++ b/Math/Optimization/Graph/Graph.php
@@ -52,7 +52,7 @@ class Graph
      */
     public function __construct() 
     {
-        $this->edges = new MultiMap(KeyType::STRICT, OrderType::LOOSE);
+        $this->edges = new MultiMap(KeyType::MULTIPLE, OrderType::LOOSE);
     }
 
     /**