diff --git a/src/Type/Definition/InterfaceType.php b/src/Type/Definition/InterfaceType.php
index 7bf37c5..dd5a6e2 100644
--- a/src/Type/Definition/InterfaceType.php
+++ b/src/Type/Definition/InterfaceType.php
@@ -49,8 +49,9 @@ class InterfaceType extends Type implements AbstractType, OutputType, CompositeT
     public static function addImplementationToInterfaces(ObjectType $impl)
     {
         self::$_lazyLoadImplementations[] = function() use ($impl) {
+            /** @var self $interface */
             foreach ($impl->getInterfaces() as $interface) {
-                $interface->_implementations[] = $impl;
+                $interface->addImplementation($impl);
             }
         };
     }
@@ -66,6 +67,16 @@ class InterfaceType extends Type implements AbstractType, OutputType, CompositeT
         self::$_lazyLoadImplementations = [];
     }
 
+    /**
+     * Add a implemented object type to interface
+     *
+     * @param ObjectType $impl
+     */
+    protected function addImplementation(ObjectType $impl)
+    {
+        $this->_implementations[] = $impl;
+    }
+
     /**
      * InterfaceType constructor.
      * @param array $config