diff --git a/Cargo.lock b/Cargo.lock
index b96d94f5..e753df39 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1522,6 +1522,7 @@ dependencies = [
 name = "ts-rs-macros"
 version = "12.0.1"
 dependencies = [
+ "indexmap",
  "proc-macro2",
  "quote",
  "syn 2.0.90",
diff --git a/macros/Cargo.toml b/macros/Cargo.toml
index 954b4cb5..87d76752 100644
--- a/macros/Cargo.toml
+++ b/macros/Cargo.toml
@@ -16,6 +16,7 @@ no-serde-warnings = []
 proc-macro = true
 
 [dependencies]
+indexmap = "2"
 proc-macro2 = "1"
 quote = "1"
 syn = { version = "2.0.28", features = ["full", "extra-traits"] }
diff --git a/macros/src/deps.rs b/macros/src/deps.rs
index ef61084a..23edcdcc 100644
--- a/macros/src/deps.rs
+++ b/macros/src/deps.rs
@@ -1,4 +1,6 @@
-use std::{collections::HashSet, rc::Rc};
+use std::rc::Rc;
+
+use indexmap::IndexSet;
 
 use proc_macro2::TokenStream;
 use quote::{quote, ToTokens};
@@ -6,8 +8,8 @@ use syn::{Path, Type};
 
 pub struct Dependencies {
     crate_rename: Rc<Path>,
-    dependencies: HashSet<Dependency>,
-    types: HashSet<Rc<Type>>,
+    dependencies: IndexSet<Dependency>,
+    types: IndexSet<Rc<Type>>,
 }
 
 #[derive(Hash, Eq, PartialEq)]
@@ -30,9 +32,9 @@ enum Dependency {
 impl Dependencies {
     pub fn new(crate_rename: Path) -> Self {
         Self {
-            dependencies: HashSet::new(),
+            dependencies: IndexSet::new(),
             crate_rename: Rc::new(crate_rename),
-            types: HashSet::new(),
+            types: IndexSet::new(),
         }
     }
 
diff --git a/macros/src/lib.rs b/macros/src/lib.rs
index b54e588e..1bc32712 100644
--- a/macros/src/lib.rs
+++ b/macros/src/lib.rs
@@ -1,7 +1,9 @@
 #![macro_use]
 #![deny(unused)]
 
-use std::collections::{HashMap, HashSet};
+use std::collections::HashMap;
+
+use indexmap::IndexSet;
 
 use proc_macro2::{Ident, TokenStream};
 use quote::{format_ident, quote};
@@ -442,7 +444,7 @@ fn generate_where_clause(
     let used_types = {
         let is_type_param = |id: &Ident| generics.type_params().any(|p| &p.ident == id);
 
-        let mut used_types = HashSet::new();
+        let mut used_types = IndexSet::new();
         for ty in dependencies.used_types() {
             used_type_params(&mut used_types, ty, is_type_param);
         }
@@ -459,7 +461,7 @@ fn generate_where_clause(
 // Associated types of a type parameter are extracted as well.
 // Note: This will not extract `I` from `I::Item`, but just `I::Item`!
 fn used_type_params<'ty, 'out>(
-    out: &'out mut HashSet<&'ty Type>,
+    out: &'out mut IndexSet<&'ty Type>,
     ty: &'ty Type,
     is_type_param: impl Fn(&'ty Ident) -> bool + Copy + 'out,
 ) {