diff --git a/Cargo.lock b/Cargo.lock
index 9435feda..4bb9a6a0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -646,6 +646,7 @@ dependencies = [
 name = "nac3artiq"
 version = "0.1.0"
 dependencies = [
+ "indexmap 2.7.1",
  "itertools",
  "nac3core",
  "nac3ld",
diff --git a/nac3artiq/Cargo.toml b/nac3artiq/Cargo.toml
index fa804659..2bceb4d2 100644
--- a/nac3artiq/Cargo.toml
+++ b/nac3artiq/Cargo.toml
@@ -9,6 +9,7 @@ name = "nac3artiq"
 crate-type = ["cdylib"]
 
 [dependencies]
+indexmap = "2.7"
 itertools = "0.14"
 pyo3 = { version = "0.21", features = ["extension-module", "gil-refs"] }
 parking_lot = "0.12"
diff --git a/nac3artiq/src/lib.rs b/nac3artiq/src/lib.rs
index 23830463..1dee8dd8 100644
--- a/nac3artiq/src/lib.rs
+++ b/nac3artiq/src/lib.rs
@@ -19,6 +19,7 @@ use std::{
     sync::Arc,
 };
 
+use indexmap::IndexMap;
 use itertools::Itertools;
 use parking_lot::{Mutex, RwLock};
 use pyo3::{
@@ -1218,8 +1219,8 @@ impl Nac3 {
         content_modules: &PySet,
     ) -> PyResult<()> {
         let (modules, class_ids) =
-            Python::with_gil(|py| -> PyResult<(HashMap<u64, PyObject>, HashSet<u64>)> {
-                let mut modules: HashMap<u64, PyObject> = HashMap::new();
+            Python::with_gil(|py| -> PyResult<(IndexMap<u64, PyObject>, HashSet<u64>)> {
+                let mut modules: IndexMap<u64, PyObject> = IndexMap::new();
                 let mut class_ids: HashSet<u64> = HashSet::new();
 
                 let id_fn = PyModule::import(py, "builtins")?.getattr("id")?;