diff --git a/Program.cs b/Program.cs
index b62240a..1483204 100644
--- a/Program.cs
+++ b/Program.cs
@@ -27,7 +27,7 @@ namespace SmallInjectorDemo
             useful2.TestTheServices();
             Console.WriteLine();
             useful3.TestTheServices();
-            Console.ReadLine();
+            //Console.ReadLine();
         }
     }
 }
\ No newline at end of file
diff --git a/SmallInjector.cs b/SmallInjector.cs
index 7b6ea80..aa95e4b 100644
--- a/SmallInjector.cs
+++ b/SmallInjector.cs
@@ -17,7 +17,7 @@ namespace SmallInjectorDemo
         /// <typeparam name="TInterface">Type of the interface of the service.</typeparam>
         /// <param name="isSingleton">True if the service should be singleton. False otherwise.</param>
         /// <param name="instance">instance of the service</param>
-        public void RegisterType<TService, TInterface>(bool isSingleton, TService instance = default(TService))
+        public void RegisterType<TService, TInterface>(bool isSingleton, TService instance = default(TService)) where TService : TInterface
         {
             _container.Add(typeof(TInterface), new RegisteredType(typeof(TService), isSingleton, null));
         }