diff --git a/ast/src/module.rs b/ast/src/module.rs
index e82e7b2c5d..b8685a2340 100644
--- a/ast/src/module.rs
+++ b/ast/src/module.rs
@@ -1,12 +1,11 @@
 use std::path::Path;
 
 use bumpalo::Bump;
-use roc_collections::all::MutMap;
 use roc_load::file::LoadedModule;
 use roc_target::TargetInfo;
 
 pub fn load_module(src_file: &Path) -> LoadedModule {
-    let subs_by_module = MutMap::default();
+    let subs_by_module = Default::default();
 
     let arena = Bump::new();
     let loaded = roc_load::file::load_and_typecheck(
diff --git a/cli/src/build.rs b/cli/src/build.rs
index 98563beedb..2d4f7fae53 100644
--- a/cli/src/build.rs
+++ b/cli/src/build.rs
@@ -4,7 +4,6 @@ use roc_build::{
     program,
 };
 use roc_builtins::bitcode;
-use roc_collections::all::MutMap;
 use roc_load::file::LoadingProblem;
 use roc_mono::ir::OptLevel;
 use roc_target::TargetInfo;
@@ -61,7 +60,7 @@ pub fn build_file<'a>(
     let target_info = TargetInfo::from(target);
 
     // Step 1: compile the app and generate the .o file
-    let subs_by_module = MutMap::default();
+    let subs_by_module = Default::default();
 
     // Release builds use uniqueness optimizations
     let stdlib = arena.alloc(roc_builtins::std::standard_stdlib());
@@ -366,7 +365,7 @@ pub fn check_file(
     let target_info = TargetInfo::default_x86_64();
 
     // Step 1: compile the app and generate the .o file
-    let subs_by_module = MutMap::default();
+    let subs_by_module = Default::default();
 
     // Release builds use uniqueness optimizations
     let stdlib = arena.alloc(roc_builtins::std::standard_stdlib());
diff --git a/compiler/constrain/src/module.rs b/compiler/constrain/src/module.rs
index a5e94f591e..3555fb2287 100644
--- a/compiler/constrain/src/module.rs
+++ b/compiler/constrain/src/module.rs
@@ -8,7 +8,20 @@ use roc_types::solved_types::{FreeVars, SolvedType};
 use roc_types::subs::{StorageSubs, VarStore, Variable};
 use roc_types::types::{Alias, Problem};
 
-pub type SubsByModule = MutMap<ModuleId, ExposedModuleTypes>;
+#[derive(Clone, Debug, Default)]
+pub struct ExposedByModule {
+    exposed: MutMap<ModuleId, ExposedModuleTypes>,
+}
+
+impl ExposedByModule {
+    pub fn insert(&mut self, module_id: ModuleId, exposed: ExposedModuleTypes) {
+        self.exposed.insert(module_id, exposed);
+    }
+
+    pub fn get(&self, module_id: &ModuleId) -> Option<&ExposedModuleTypes> {
+        self.exposed.get(module_id)
+    }
+}
 
 #[derive(Clone, Debug)]
 pub enum ExposedModuleTypes {
@@ -119,7 +132,7 @@ pub fn pre_constrain_imports(
     home: ModuleId,
     references: &MutSet<Symbol>,
     imported_modules: MutMap<ModuleId, Region>,
-    exposed_types: &mut SubsByModule,
+    exposed_types: &mut ExposedByModule,
     stdlib: &StdLib,
 ) -> ConstrainableImports {
     let mut imported_symbols = Vec::with_capacity(references.len());
diff --git a/compiler/load/src/file.rs b/compiler/load/src/file.rs
index fee4793e13..70dc5921e3 100644
--- a/compiler/load/src/file.rs
+++ b/compiler/load/src/file.rs
@@ -11,7 +11,7 @@ use roc_can::module::{canonicalize_module_defs, Module};
 use roc_collections::all::{default_hasher, BumpMap, MutMap, MutSet};
 use roc_constrain::module::{
     constrain_imports, constrain_module, pre_constrain_imports, ConstrainableImports,
-    ExposedModuleTypes, HackyImport, Import, SubsByModule,
+    ExposedByModule, ExposedModuleTypes, HackyImport, Import,
 };
 use roc_module::ident::{Ident, ModuleName, QualifiedModuleName};
 use roc_module::symbol::{
@@ -567,7 +567,7 @@ struct State<'a> {
     pub platform_data: Option<PlatformData>,
     pub goal_phase: Phase,
     pub stdlib: &'a StdLib,
-    pub exposed_types: SubsByModule,
+    pub exposed_types: ExposedByModule,
     pub output_path: Option<&'a str>,
     pub platform_path: PlatformPath<'a>,
     pub target_info: TargetInfo,
@@ -607,7 +607,7 @@ impl<'a> State<'a> {
         target_info: TargetInfo,
         goal_phase: Phase,
         stdlib: &'a StdLib,
-        exposed_types: SubsByModule,
+        exposed_types: ExposedByModule,
         arc_modules: Arc<Mutex<PackageModuleIds<'a>>>,
         ident_ids_by_module: Arc<Mutex<MutMap<ModuleId, IdentIds>>>,
     ) -> Self {
@@ -813,7 +813,7 @@ pub fn load_and_typecheck<'a>(
     filename: PathBuf,
     stdlib: &'a StdLib,
     src_dir: &Path,
-    exposed_types: SubsByModule,
+    exposed_types: ExposedByModule,
     target_info: TargetInfo,
 ) -> Result<LoadedModule, LoadingProblem<'a>> {
     use LoadResult::*;
@@ -840,7 +840,7 @@ pub fn load_and_monomorphize<'a>(
     filename: PathBuf,
     stdlib: &'a StdLib,
     src_dir: &Path,
-    exposed_types: SubsByModule,
+    exposed_types: ExposedByModule,
     target_info: TargetInfo,
 ) -> Result<MonomorphizedModule<'a>, LoadingProblem<'a>> {
     use LoadResult::*;
@@ -868,7 +868,7 @@ pub fn load_and_monomorphize_from_str<'a>(
     src: &'a str,
     stdlib: &'a StdLib,
     src_dir: &Path,
-    exposed_types: SubsByModule,
+    exposed_types: ExposedByModule,
     target_info: TargetInfo,
 ) -> Result<MonomorphizedModule<'a>, LoadingProblem<'a>> {
     use LoadResult::*;
@@ -1034,7 +1034,7 @@ fn load<'a>(
     load_start: LoadStart<'a>,
     stdlib: &'a StdLib,
     src_dir: &Path,
-    exposed_types: SubsByModule,
+    exposed_types: ExposedByModule,
     goal_phase: Phase,
     target_info: TargetInfo,
 ) -> Result<LoadResult<'a>, LoadingProblem<'a>> {
@@ -1070,7 +1070,7 @@ fn load_single_threaded<'a>(
     load_start: LoadStart<'a>,
     stdlib: &'a StdLib,
     src_dir: &Path,
-    exposed_types: SubsByModule,
+    exposed_types: ExposedByModule,
     goal_phase: Phase,
     target_info: TargetInfo,
 ) -> Result<LoadResult<'a>, LoadingProblem<'a>> {
@@ -1246,7 +1246,7 @@ fn load_multi_threaded<'a>(
     load_start: LoadStart<'a>,
     stdlib: &'a StdLib,
     src_dir: &Path,
-    exposed_types: SubsByModule,
+    exposed_types: ExposedByModule,
     goal_phase: Phase,
     target_info: TargetInfo,
 ) -> Result<LoadResult<'a>, LoadingProblem<'a>> {
@@ -3041,7 +3041,7 @@ impl<'a> BuildTask<'a> {
         constraint: ConstraintSoa,
         var_store: VarStore,
         imported_modules: MutMap<ModuleId, Region>,
-        exposed_types: &mut SubsByModule,
+        exposed_types: &mut ExposedByModule,
         stdlib: &StdLib,
         dep_idents: MutMap<ModuleId, IdentIds>,
         declarations: Vec<Declaration>,
diff --git a/compiler/load/tests/test_load.rs b/compiler/load/tests/test_load.rs
index 4c77e2e00c..e1ab310efb 100644
--- a/compiler/load/tests/test_load.rs
+++ b/compiler/load/tests/test_load.rs
@@ -19,7 +19,7 @@ mod test_load {
     use roc_can::def::Declaration::*;
     use roc_can::def::Def;
     use roc_collections::all::MutMap;
-    use roc_constrain::module::SubsByModule;
+    use roc_constrain::module::ExposedByModule;
     use roc_load::file::LoadedModule;
     use roc_module::ident::ModuleName;
     use roc_module::symbol::{Interns, ModuleId};
@@ -159,7 +159,7 @@ mod test_load {
     fn load_fixture(
         dir_name: &str,
         module_name: &str,
-        subs_by_module: SubsByModule,
+        subs_by_module: ExposedByModule,
     ) -> LoadedModule {
         let src_dir = fixtures_dir().join(dir_name);
         let filename = src_dir.join(format!("{}.roc", module_name));
diff --git a/docs/src/lib.rs b/docs/src/lib.rs
index 5749caf14c..9d4c88ac08 100644
--- a/docs/src/lib.rs
+++ b/docs/src/lib.rs
@@ -426,7 +426,7 @@ pub fn load_modules_for_files(filenames: Vec<PathBuf>, std_lib: StdLib) -> Vec<L
             filename,
             &std_lib,
             src_dir.as_path(),
-            MutMap::default(),
+            Default::default(),
             roc_target::TargetInfo::default_x86_64(), // This is just type-checking for docs, so "target" doesn't matter
         ) {
             Ok(loaded) => modules.push(loaded),
diff --git a/repl_eval/src/gen.rs b/repl_eval/src/gen.rs
index a11ba966b8..932ae40bf3 100644
--- a/repl_eval/src/gen.rs
+++ b/repl_eval/src/gen.rs
@@ -1,7 +1,6 @@
 use bumpalo::Bump;
 use std::path::{Path, PathBuf};
 
-use roc_collections::all::MutMap;
 use roc_fmt::annotation::Formattable;
 use roc_fmt::annotation::{Newlines, Parens};
 use roc_load::file::{LoadingProblem, MonomorphizedModule};
@@ -55,7 +54,7 @@ pub fn compile_to_mono<'a>(
 
     let module_src = arena.alloc(promote_expr_to_module(src));
 
-    let exposed_types = MutMap::default();
+    let exposed_types = Default::default();
     let loaded = roc_load::file::load_and_monomorphize_from_str(
         arena,
         filename,