diff --git a/patterns/structural/flyweight_with_metaclass.py b/patterns/structural/flyweight_with_metaclass.py
index ced8d915..79844234 100644
--- a/patterns/structural/flyweight_with_metaclass.py
+++ b/patterns/structural/flyweight_with_metaclass.py
@@ -19,12 +19,11 @@ def __new__(mcs, name, parents, dct):
     def _serialize_params(cls, *args, **kwargs):
         """
         Serialize input parameters to a key.
-        Simple implementation is just to serialize it as a string
+        Simple implementation is just to serialize it as a string. ``repr`` keeps
+        ``("1", "0")``, ``("10",)`` and ``(1,)`` apart, and sorting the keyword
+        arguments makes the key independent of their order.
         """
-        args_list = list(map(str, args))
-        args_list.extend([str(kwargs), cls.__name__])
-        key = "".join(args_list)
-        return key
+        return repr((cls.__name__, args, sorted(kwargs.items())))
 
     def __call__(cls, *args, **kwargs):
         key = FlyweightMeta._serialize_params(cls, *args, **kwargs)
diff --git a/tests/structural/test_flyweight_with_metaclass.py b/tests/structural/test_flyweight_with_metaclass.py
new file mode 100644
index 00000000..5a342182
--- /dev/null
+++ b/tests/structural/test_flyweight_with_metaclass.py
@@ -0,0 +1,26 @@
+from patterns.structural.flyweight_with_metaclass import Card2
+
+
+def test_same_arguments_share_an_instance():
+    Card2.pool.clear()
+    assert Card2("10", "h", a=1) is Card2("10", "h", a=1)
+
+
+def test_different_arguments_do_not_share_an_instance():
+    Card2.pool.clear()
+    assert Card2("10", "h", a=1) is not Card2("10", "h", a=2)
+
+
+def test_argument_boundaries_are_part_of_the_key():
+    Card2.pool.clear()
+    assert Card2("1", "0") is not Card2("10")
+
+
+def test_argument_types_are_part_of_the_key():
+    Card2.pool.clear()
+    assert Card2(1) is not Card2("1")
+
+
+def test_keyword_argument_order_does_not_matter():
+    Card2.pool.clear()
+    assert Card2(a=1, b=2) is Card2(b=2, a=1)