diff --git a/src/nitypes/waveform/_digital/_signal.py b/src/nitypes/waveform/_digital/_signal.py
index 8414c5c..79b7ee2 100644
--- a/src/nitypes/waveform/_digital/_signal.py
+++ b/src/nitypes/waveform/_digital/_signal.py
@@ -33,9 +33,13 @@ def __init__(
         self,
         owner: DigitalWaveform[TDigitalState],
         signal_index: SupportsIndex,
-        column_index: SupportsIndex,
+        column_index: SupportsIndex | None = None,
     ) -> None:
         """Initialize a new digital waveform signal."""
+        if column_index is None:
+            # when unpickling an old version, column_index may not be provided
+            column_index = signal_index
+
         self._owner = owner
         self._signal_index = arg_to_uint("signal index", signal_index)
         self._column_index = arg_to_uint("column index", column_index)
diff --git a/src/nitypes/waveform/_digital/_waveform.py b/src/nitypes/waveform/_digital/_waveform.py
index a7f8d75..7d54214 100644
--- a/src/nitypes/waveform/_digital/_waveform.py
+++ b/src/nitypes/waveform/_digital/_waveform.py
@@ -838,6 +838,9 @@ def __init__(
         ):
             extended_properties = ExtendedPropertyDictionary(extended_properties)
         self._extended_properties = extended_properties
+        if not hasattr(self._extended_properties, "_on_key_changed"):
+            # when unpickling an old version, _on_key_changed may not exist
+            self._extended_properties._on_key_changed = []
         self._extended_properties._on_key_changed.append(
             weakref.WeakMethod(self._on_extended_property_changed)
         )
diff --git a/tests/unit/waveform/test_digital_waveform.py b/tests/unit/waveform/test_digital_waveform.py
index d2fe884..94e2b79 100644
--- a/tests/unit/waveform/test_digital_waveform.py
+++ b/tests/unit/waveform/test_digital_waveform.py
@@ -1976,10 +1976,6 @@ def test___waveform___pickle___references_public_modules() -> None:
                 extended_properties={"NI_ChannelName": "Dev1/ai0", "NI_UnitDescription": "Volts"},
                 timing=Timing.create_with_regular_interval(dt.timedelta(milliseconds=1)),
             ),
-            marks=pytest.mark.xfail(
-                raises=AttributeError,
-                reason="https://github.com/ni/nitypes-python/issues/234 - ExtendedPropertyDictionary._on_key_changed breaks pickle compatibility",
-            ),
         ),
         # nitypes 1.0.1
         (
diff --git a/tests/unit/waveform/test_digital_waveform_signal.py b/tests/unit/waveform/test_digital_waveform_signal.py
index e617438..5fa7f4b 100644
--- a/tests/unit/waveform/test_digital_waveform_signal.py
+++ b/tests/unit/waveform/test_digital_waveform_signal.py
@@ -378,10 +378,6 @@ def test___waveform___pickle___references_public_modules() -> None:
             DigitalWaveform(
                 3, 2, extended_properties={"NI_LineNames": "port0/line1, port0/line0"}
             ).signals[1],
-            marks=pytest.mark.xfail(
-                raises=AttributeError,
-                reason="https://github.com/ni/nitypes-python/issues/234 - ExtendedPropertyDictionary._on_key_changed breaks pickle compatibility",
-            ),
         ),
         # nitypes 1.0.1
         (