diff --git a/tests/test_add_connections.py b/tests/test_add_connections.py
index 5fa8f7f..9d03522 100644
--- a/tests/test_add_connections.py
+++ b/tests/test_add_connections.py
@@ -463,3 +463,63 @@ def test_combine_error():
         znflow.combine([1, 2, 3], attribute="outs", only_getattr_on_nodes=False)
 
     assert znflow.combine([1, 2, 3], attribute="outs") == [1, 2, 3]
+
+
+def test_append_connection():
+    with znflow.DiGraph():
+        a = CreateList(size=5)
+        b = CreateList(size=4)
+
+        assert isinstance(a.outs, znflow.Connection)
+
+        with pytest.raises(TypeError):
+            a.outs.append(b.outs)
+
+
+def test_extend_connection():
+    with znflow.DiGraph():
+        a = CreateList(size=5)
+        b = CreateList(size=4)
+
+        with pytest.raises(TypeError):
+            a.outs.extend(b.outs)
+
+
+def test_append_function_future():
+    with znflow.DiGraph():
+        a = create_list(5)
+        b = create_list(5)
+
+        assert isinstance(a, znflow.FunctionFuture)
+
+        with pytest.raises(TypeError):
+            a.append(b)
+
+
+def test_extend_function_future():
+    with znflow.DiGraph():
+        a = create_list(5)
+        b = create_list(5)
+
+        with pytest.raises(TypeError):
+            a.extend(b)
+
+
+def test_append_combined_connection():
+    with znflow.DiGraph():
+        a = create_list(5)
+        b = create_list(5)
+
+        assert isinstance(a + b, znflow.CombinedConnections)
+
+        with pytest.raises(TypeError):
+            a.append(a + b)
+
+
+def test_extend_combined_connection():
+    with znflow.DiGraph():
+        a = create_list(5)
+        b = create_list(5)
+
+        with pytest.raises(TypeError):
+            a.extend(a + b)
diff --git a/znflow/base.py b/znflow/base.py
index 80e83f4..0c72baf 100644
--- a/znflow/base.py
+++ b/znflow/base.py
@@ -268,6 +268,24 @@ def __iter__(self):
         except AttributeError:
             raise TypeError(f"'{self}' object is not iterable")
 
+    def extend(self, *args) -> None:
+        """
+        Raises
+        ------
+        TypeError
+            If the method is called.
+        """
+        raise TypeError("Connections can not be extended. Use 'self += other' instead.")
+
+    def append(self, *args) -> None:
+        """
+        Raises
+        ------
+        TypeError
+            If the method is called.
+        """
+        raise TypeError("Connections can not be appended.")
+
 
 @dataclasses.dataclass(frozen=True)
 class CombinedConnections:
@@ -350,6 +368,26 @@ def result(self):
                 f" only supported type is list. Please change {connection}"
             ) from err
 
+    def extend(self, *args) -> None:
+        """
+        Raises
+        ------
+        TypeError
+            If the method is called.
+        """
+        raise TypeError(
+            "CombinedConnections can not be extended. Use 'self += other' instead."
+        )
+
+    def append(self, *args) -> None:
+        """
+        Raises
+        ------
+        TypeError
+            If the method is called.
+        """
+        raise TypeError("CombinedConnections can not be appended.")
+
 
 @dataclasses.dataclass
 class FunctionFuture(NodeBaseMixin):
@@ -436,3 +474,23 @@ def __iter__(self):
             return resolve(self).__iter__()
         except AttributeError:
             raise TypeError(f"'{self}' object is not iterable")
+
+    def extend(self, *args) -> None:
+        """
+        Raises
+        ------
+        TypeError
+            If the method is called.
+        """
+        raise TypeError(
+            "FunctionFuture can not be extended. Use 'self += other' instead."
+        )
+
+    def append(self, *args) -> None:
+        """
+        Raises
+        ------
+        TypeError
+            If the method is called.
+        """
+        raise TypeError("FunctionFuture can not be appended.")