diff --git a/simlib/mixnet-sims/src/node/mix/state.rs b/simlib/mixnet-sims/src/node/mix/state.rs
index ced1420..e075344 100644
--- a/simlib/mixnet-sims/src/node/mix/state.rs
+++ b/simlib/mixnet-sims/src/node/mix/state.rs
@@ -3,7 +3,7 @@ use std::any::Any;
 use serde::Serialize;
 
 use netrunner::{
-    node::NodeId,
+    node::{serialize_node_id_as_index, NodeId},
     output_processors::{Record, RecordType, Runtime},
     settings::SimulationSettings,
     warding::SimulationState,
@@ -11,6 +11,7 @@ use netrunner::{
 
 #[derive(Debug, Clone, Serialize)]
 pub struct MixnodeState {
+    #[serde(serialize_with = "serialize_node_id_as_index")]
     pub node_id: NodeId,
     pub step_id: usize,
     pub num_messages_broadcasted: usize,
diff --git a/simlib/netrunner/src/node/mod.rs b/simlib/netrunner/src/node/mod.rs
index 2de43cd..c5b1c0e 100644
--- a/simlib/netrunner/src/node/mod.rs
+++ b/simlib/netrunner/src/node/mod.rs
@@ -189,3 +189,10 @@ impl NodeIdExt for NodeId {
         NodeId::new(bytes)
     }
 }
+
+pub fn serialize_node_id_as_index<S>(id: &NodeId, s: S) -> Result<S::Ok, S::Error>
+where
+    S: serde::Serializer,
+{
+    s.serialize_u64(id.index() as u64)
+}