diff --git a/Cargo.toml b/Cargo.toml
index 40939a2..d223761 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ome-metadata"
-version = "0.2.1"
+version = "0.2.2"
 edition = "2024"
 rust-version = "1.85.1"
 authors = ["Wim Pomp <w.pomp@nki.nl>"]
diff --git a/py/ome_metadata/__init__.py b/py/ome_metadata/__init__.py
index d96f131..cfbb99e 100644
--- a/py/ome_metadata/__init__.py
+++ b/py/ome_metadata/__init__.py
@@ -27,6 +27,12 @@ class Ome(UserDict):
         else:
             return new
 
+    def __getstate__(self) -> dict[str, Any]:
+        return self.data
+
+    def __setstate__(self, state: dict[str, Any]) -> None:
+        self.data = state
+
 
 class OmeList(UserList):
     def __getitem__(self, item: int) -> Ome | OmeList | int | float | str:
diff --git a/src/py.rs b/src/py.rs
index 72c0343..ca37cb5 100644
--- a/src/py.rs
+++ b/src/py.rs
@@ -1,4 +1,3 @@
-use anyhow::anyhow;
 use crate::Ome;
 use crate::ome::{
     Convert, UnitsElectricPotential, UnitsFrequency, UnitsLength, UnitsPower,
@@ -6,39 +5,7 @@ use crate::ome::{
 };
 use pyo3::exceptions::PyValueError;
 use pyo3::prelude::*;
-use pyo3::IntoPyObjectExt;
 
-/// helper class to be used for unpickling
-#[pyclass(module = "ome_metadata.ome_metadata_rs")]
-struct Constructor;
-
-#[pymethods]
-impl Constructor {
-    #[new]
-    fn new() -> Self {
-        Self
-    }
-
-    fn __getstate__(&self) -> (u8,) {
-        (0,)
-    }
-
-    fn __setstate__(&self, _state: (u8,)) {}
-
-    #[staticmethod]
-    fn __call__(py: Python, class: String, variant: String) -> PyResult<Bound<PyAny>> {
-        match class.as_str() {
-            "ElectricPotential" => ElectricPotential::new(&variant)?.into_bound_py_any(py),
-            "Frequency" => Frequency::new(&variant)?.into_bound_py_any(py),
-            "Length" => Length::new(&variant)?.into_bound_py_any(py),
-            "Power" => Power::new(&variant)?.into_bound_py_any(py),
-            "Pressure" => Pressure::new(&variant)?.into_bound_py_any(py),
-            "Temperature" => Temperature::new(&variant)?.into_bound_py_any(py),
-            "Time" => Time::new(&variant)?.into_bound_py_any(py),
-            _ => Err(anyhow!("cannot parse class {}", class).into())
-        }
-    }
-}
 
 macro_rules! impl_enum_into_py_object {
     ($($s:ident: $t:ty $(,)?)*) => {
@@ -79,9 +46,9 @@ macro_rules! impl_enum_into_py_object {
                 fn __str__(&self) -> String {
                     format!("{:?}", self.inner)
                 }
-
-                fn __reduce__(&self) -> PyResult<(Constructor, (String, String))> {
-                    Ok((Constructor, (stringify!($s).to_string(), format!("{:?}", self.inner))))
+                
+                fn __getnewargs__(&self) -> (String,) {
+                    (format!("{:?}", self.inner),)
                 }
             }
 
@@ -110,7 +77,6 @@ impl_enum_into_py_object! {
 #[pymodule]
 #[pyo3(name = "ome_metadata_rs")]
 fn ome_metadata_rs(m: &Bound<'_, PyModule>) -> PyResult<()> {
-    m.add_class::<Constructor>()?;
     m.add_class::<ElectricPotential>()?;
     m.add_class::<Frequency>()?;
     m.add_class::<Length>()?;