diff --git a/skcriteria/utils/bunch.py b/skcriteria/utils/bunch.py
index 3e1da1a..f9aedd9 100644
--- a/skcriteria/utils/bunch.py
+++ b/skcriteria/utils/bunch.py
@@ -46,17 +46,14 @@ class Bunch(Mapping):
     >>> b.a = 3
     >>> b['a']
     3
-    >>> b.c = 6
-    >>> b['c']
-    6
 
     """
 
     def __init__(self, name, data):
         if not isinstance(data, Mapping):
             raise TypeError("Data must be some kind of mapping")
-        self._name = str(name)
-        self._data = data
+        super().__setattr__("_name", str(name))
+        super().__setattr__("_data", data)
 
     def __getitem__(self, k):
         """x.__getitem__(y) <==> x[y]."""
@@ -69,6 +66,10 @@ def __getattr__(self, a):
         except KeyError:
             raise AttributeError(a)
 
+    def __setattr__(self, a, v):
+        """x.__setattr__(a, v) <==> x.a = v."""
+        raise AttributeError(f"Bunch {self._name!r} is read-only")
+
     def __copy__(self):
         """x.__copy__() <==> copy.copy(x)."""
         cls = type(self)
@@ -87,7 +88,7 @@ def __deepcopy__(self, memo):
         memo[id(self)] = clone
 
         # now we copy the data
-        clone._data = copy.deepcopy(self._data, memo)
+        super(cls, clone).__setattr__("_data", copy.deepcopy(self._data, memo))
 
         return clone
 
diff --git a/tests/utils/test_bunch.py b/tests/utils/test_bunch.py
index 9e97286..a5fa8cf 100644
--- a/tests/utils/test_bunch.py
+++ b/tests/utils/test_bunch.py
@@ -91,3 +91,9 @@ def test_Bunch_copy():
 def test_Bunch_data_is_not_a_mapping():
     with pytest.raises(TypeError, match="Data must be some kind of mapping"):
         bunch.Bunch("foo", None)
+
+
+def test_Bunch_assign_fails():
+    foo_bunch = bunch.Bunch("foo", {})
+    with pytest.raises(AttributeError, match="Bunch 'foo' is read-only"):
+        foo_bunch.some_key = 1