diff --git a/monads/maybe.py b/monads/maybe.py
index edd959f..9ac2e6b 100644
--- a/monads/maybe.py
+++ b/monads/maybe.py
@@ -120,9 +120,6 @@ class Just(Maybe[T]):
     def __repr__(self) -> str:  # pragma: no cover
         return f"<Just {self.value}>"
 
-    def __sizeof__(self) -> int:
-        return 1
-
     def __len__(self) -> int:
         return 1
 
@@ -151,9 +148,6 @@ class Nothing(Maybe[T]):
     def __repr__(self) -> str:  # pragma: no cover
         return "<Nothing>"
 
-    def __sizeof__(self) -> int:
-        return 0
-
     def __len__(self) -> int:
         return 0
 
diff --git a/tests/test_maybe.py b/tests/test_maybe.py
index 0b73e00..a41c3f6 100644
--- a/tests/test_maybe.py
+++ b/tests/test_maybe.py
@@ -155,3 +155,6 @@ def test_flatten() -> None:
     m_empty: Maybe[Maybe[str]] = Just(Nothing())
     m_flat: Maybe[str] = m_empty.flatten()
     assert m_flat.or_else("backup") == "backup"
+
+    m_full: Maybe[Maybe[str]] = Just(Just("becon"))
+    assert m_full.flatten().or_else("backup") == "becon"