diff --git a/crates/aiken-lang/src/builtins.rs b/crates/aiken-lang/src/builtins.rs
index 3d426d8b..dfd4c093 100644
--- a/crates/aiken-lang/src/builtins.rs
+++ b/crates/aiken-lang/src/builtins.rs
@@ -1,9 +1,3 @@
-use std::{cell::RefCell, collections::HashMap, sync::Arc};
-
-use strum::IntoEnumIterator;
-
-use uplc::builtins::DefaultFunction;
-
 use crate::{
     ast::{Arg, ArgName, CallArg, Function, ModuleKind, Span, TypedDataType, TypedFunction, UnOp},
     builder::{DataTypeKey, FunctionAccessKey},
@@ -14,6 +8,10 @@ use crate::{
     },
     IdGenerator,
 };
+use indexmap::IndexMap;
+use std::{cell::RefCell, collections::HashMap, sync::Arc};
+use strum::IntoEnumIterator;
+use uplc::builtins::DefaultFunction;
 
 pub const BYTE_ARRAY: &str = "ByteArray";
 pub const BOOL: &str = "Bool";
@@ -533,8 +531,8 @@ pub fn from_default_function(
     })
 }
 
-pub fn prelude_functions(id_gen: &IdGenerator) -> HashMap<FunctionAccessKey, TypedFunction> {
-    let mut functions = HashMap::new();
+pub fn prelude_functions(id_gen: &IdGenerator) -> IndexMap<FunctionAccessKey, TypedFunction> {
+    let mut functions = IndexMap::new();
 
     // /// Negate the argument. Useful for map/fold and pipelines.
     // pub fn not(self: Bool) -> Bool {
@@ -800,8 +798,8 @@ pub fn prelude_functions(id_gen: &IdGenerator) -> HashMap<FunctionAccessKey, Typ
     functions
 }
 
-pub fn prelude_data_types(id_gen: &IdGenerator) -> HashMap<DataTypeKey, TypedDataType> {
-    let mut data_types = HashMap::new();
+pub fn prelude_data_types(id_gen: &IdGenerator) -> IndexMap<DataTypeKey, TypedDataType> {
+    let mut data_types = IndexMap::new();
 
     // Option
     let option_data_type = TypedDataType::option(generic_var(id_gen.next()));
diff --git a/crates/aiken-lang/src/uplc.rs b/crates/aiken-lang/src/uplc.rs
index 806dee1e..d4738d8b 100644
--- a/crates/aiken-lang/src/uplc.rs
+++ b/crates/aiken-lang/src/uplc.rs
@@ -44,7 +44,7 @@ pub struct CodeGenerator<'a> {
     defined_functions: IndexMap<FunctionAccessKey, ()>,
     functions: IndexMap<FunctionAccessKey, &'a TypedFunction>,
     data_types: IndexMap<DataTypeKey, &'a TypedDataType>,
-    module_types: &'a IndexMap<String, TypeInfo>,
+    module_types: IndexMap<&'a String, &'a TypeInfo>,
     id_gen: IdGenerator,
     needs_field_access: bool,
     used_data_assert_on_list: bool,
@@ -55,7 +55,7 @@ impl<'a> CodeGenerator<'a> {
     pub fn new(
         functions: IndexMap<FunctionAccessKey, &'a TypedFunction>,
         data_types: IndexMap<DataTypeKey, &'a TypedDataType>,
-        module_types: &'a IndexMap<String, TypeInfo>,
+        module_types: IndexMap<&'a String, &'a TypeInfo>,
     ) -> Self {
         CodeGenerator {
             defined_functions: IndexMap::new(),
diff --git a/crates/aiken-project/src/blueprint/validator.rs b/crates/aiken-project/src/blueprint/validator.rs
index 814d4202..73e825e3 100644
--- a/crates/aiken-project/src/blueprint/validator.rs
+++ b/crates/aiken-project/src/blueprint/validator.rs
@@ -166,6 +166,7 @@ mod test {
         IdGenerator,
     };
     use assert_json_diff::assert_json_eq;
+    use indexmap::IndexMap;
     use serde_json::{self, json};
     use std::{collections::HashMap, path::PathBuf};
 
@@ -176,8 +177,8 @@ mod test {
         package: PackageName,
         id_gen: IdGenerator,
         module_types: HashMap<String, TypeInfo>,
-        functions: HashMap<FunctionAccessKey, TypedFunction>,
-        data_types: HashMap<DataTypeKey, TypedDataType>,
+        functions: IndexMap<FunctionAccessKey, TypedFunction>,
+        data_types: IndexMap<DataTypeKey, TypedDataType>,
     }
 
     impl TestProject {
diff --git a/crates/aiken-project/src/lib.rs b/crates/aiken-project/src/lib.rs
index 6bd6cbc5..e3172ca8 100644
--- a/crates/aiken-project/src/lib.rs
+++ b/crates/aiken-project/src/lib.rs
@@ -65,8 +65,8 @@ where
     sources: Vec<Source>,
     pub warnings: Vec<Warning>,
     event_listener: T,
-    functions: HashMap<FunctionAccessKey, TypedFunction>,
-    data_types: HashMap<DataTypeKey, TypedDataType>,
+    functions: IndexMap<FunctionAccessKey, TypedFunction>,
+    data_types: IndexMap<DataTypeKey, TypedDataType>,
 }
 
 impl<T> Project<T>
diff --git a/crates/aiken-project/src/module.rs b/crates/aiken-project/src/module.rs
index c083bc30..f4417276 100644
--- a/crates/aiken-project/src/module.rs
+++ b/crates/aiken-project/src/module.rs
@@ -9,6 +9,7 @@ use aiken_lang::{
     uplc::CodeGenerator,
     VALIDATOR_NAMES,
 };
+use indexmap::IndexMap;
 use petgraph::{algo, graph::NodeIndex, Direction, Graph};
 use std::{
     collections::{HashMap, HashSet},
@@ -272,16 +273,16 @@ impl CheckedModules {
 
     pub fn new_generator<'a>(
         &'a self,
-        builtin_functions: &'a HashMap<FunctionAccessKey, TypedFunction>,
-        builtin_data_types: &'a HashMap<DataTypeKey, TypedDataType>,
+        builtin_functions: &'a IndexMap<FunctionAccessKey, TypedFunction>,
+        builtin_data_types: &'a IndexMap<DataTypeKey, TypedDataType>,
         module_types: &'a HashMap<String, TypeInfo>,
     ) -> CodeGenerator<'a> {
-        let mut functions = HashMap::new();
+        let mut functions = IndexMap::new();
         for (k, v) in builtin_functions {
             functions.insert(k.clone(), v);
         }
 
-        let mut data_types = HashMap::new();
+        let mut data_types = IndexMap::new();
         for (k, v) in builtin_data_types {
             data_types.insert(k.clone(), v);
         }
@@ -316,7 +317,11 @@ impl CheckedModules {
                 }
             }
         }
-        CodeGenerator::new(functions, data_types, module_types)
+
+        let mut module_types_index = IndexMap::new();
+        module_types_index.extend(module_types);
+
+        CodeGenerator::new(functions, data_types, module_types_index)
     }
 }