diff --git a/lakers-python/README.md b/lakers-python/README.md
index abc0eabd..227dcfb6 100644
--- a/lakers-python/README.md
+++ b/lakers-python/README.md
@@ -42,7 +42,7 @@ To deploy:
 ln -s ../examples ./examples
 MATURIN_PYPI_TOKEN=<your pypi token here> maturin publish
 ```
-
+.take().ok_or(StateMismatch)?,
 ## Requirements
 
 The maturin executable must be available. The recommended way is to install and use it in a virtual environment:
diff --git a/lakers-python/src/initiator.rs b/lakers-python/src/initiator.rs
index aaa46468..c158aaca 100644
--- a/lakers-python/src/initiator.rs
+++ b/lakers-python/src/initiator.rs
@@ -144,7 +144,7 @@ impl PyEdhocInitiator {
     }
 
     pub fn completed_without_message_4<'a>(&mut self, py: Python<'a>) -> PyResult<()> {
-        match i_complete_without_message_4(&self.wait_m4) {
+        match i_complete_without_message_4(&self.wait_m4.take().ok_or(StateMismatch)?) {
             Ok(state) => {
                 self.completed = Some(state);
                 Ok(())
@@ -160,7 +160,7 @@ impl PyEdhocInitiator {
     ) -> PyResult<Option<EADItem>> {
         let message_4 = EdhocMessageBuffer::new_from_slice(message_4.as_slice())?;
 
-        match i_process_message_4(&mut self.wait_m4, &mut default_crypto(), &message_4) {
+        match i_process_message_4(&mut self.wait_m4.take().ok_or(StateMismatch)?, &mut default_crypto(), &message_4) {
             Ok((state, ead_4)) => {
                 self.completed = Some(state);
                 Ok(ead_4)
diff --git a/lakers-python/src/responder.rs b/lakers-python/src/responder.rs
index 0c545b33..c861138c 100644
--- a/lakers-python/src/responder.rs
+++ b/lakers-python/src/responder.rs
@@ -140,7 +140,7 @@ impl PyEdhocResponder {
         py: Python<'a>,
         ead_4: Option<EADItem>,
     ) -> PyResult<Bound<'a, PyBytes>> {
-        match r_prepare_message_4(&self.processed_m3, &mut default_crypto(), &ead_4) {
+        match r_prepare_message_4(&self.processed_m3.take().ok_or(StateMismatch)?, &mut default_crypto(), &ead_4) {
             Ok((state, message_4)) => {
                 self.completed = Some(state);
                 Ok(PyBytes::new_bound(py, message_4.as_slice()))
@@ -150,7 +150,7 @@ impl PyEdhocResponder {
     }
 
     pub fn completed_without_message_4<'a>(&mut self, py: Python<'a>) -> PyResult<()> {
-        match r_complete_without_message_4(&self.processed_m3) {
+        match r_complete_without_message_4(&self.processed_m3.take().ok_or(StateMismatch)?) {
             Ok(state) => {
                 self.completed = Some(state);
                 Ok(())
diff --git a/lakers-python/test/test_lakers.py b/lakers-python/test/test_lakers.py
index 9dc93715..710445ff 100644
--- a/lakers-python/test/test_lakers.py
+++ b/lakers-python/test/test_lakers.py
@@ -69,6 +69,10 @@ def _test_handshake(cred_r_transfer, cred_i_transfer):
 
     assert i_prk_out == r_prk_out
 
+    # advanced state
+    responder.completed_without_message_4()
+    initiator.completed_without_message_4()
+
     i_oscore_secret = initiator.edhoc_exporter(0, [], 16)
     i_oscore_salt = initiator.edhoc_exporter(1, [], 8)
     r_oscore_secret = responder.edhoc_exporter(0, [], 16)