diff --git a/include/System/OverlayManager.hpp b/include/System/OverlayManager.hpp
index e56ea58e..9c840c3d 100644
--- a/include/System/OverlayManager.hpp
+++ b/include/System/OverlayManager.hpp
@@ -240,6 +240,7 @@ typedef u32 OverlayId;
 
 typedef u32 OverlayIndex;
 enum OverlayIndex_ {
+    /*  -1 */ OverlayIndex_None = -1,
     /* 000 */ OverlayIndex_Second,
     /* 001 */ OverlayIndex_SceneInit,
     /* 002 */ OverlayIndex_Collect,
@@ -382,11 +383,11 @@ enum OverlaySlot_ {
 
 class OverlayManager {
   public:
-    OverlayId mLoadedOverlays[OverlaySlot_COUNT];
+    OverlayIndex mLoadedOverlays[OverlaySlot_COUNT];
 
-    void Load(OverlaySlot index, OverlayId id);
-    void LoadIfNotLoaded(OverlaySlot index, OverlayId id);
-    void Unload(OverlaySlot index);
+    void Load(OverlaySlot slot, OverlayIndex index);
+    void LoadIfNotLoaded(OverlaySlot slot, OverlayIndex index);
+    void Unload(OverlaySlot slot);
     void LoadOverlaySetup(s32 index);
     void UnloadOverlaySetup();
 
diff --git a/src/Main/System/OverlayManager.cpp b/src/Main/System/OverlayManager.cpp
index 7bdc50cd..8b42d3ee 100644
--- a/src/Main/System/OverlayManager.cpp
+++ b/src/Main/System/OverlayManager.cpp
@@ -28,29 +28,29 @@ extern u32* data_027e0ce0[];
 extern "C" void func_ov007_02102850(u32**);
 extern "C" void func_ov007_021028a0(u32**);
 
-THUMB void OverlayManager::LoadIfNotLoaded(OverlaySlot index, OverlayId id) {
-    OverlayId loadedId = gOverlayManager.mLoadedOverlays[index];
+THUMB void OverlayManager::LoadIfNotLoaded(OverlaySlot slot, OverlayIndex index) {
+    OverlayIndex loadedIndex = gOverlayManager.mLoadedOverlays[slot];
 
-    if (id != loadedId) {
-        this->Unload(index);
-        this->Load(index, id);
+    if (index != loadedIndex) {
+        this->Unload(slot);
+        this->Load(slot, index);
     }
 }
 
-THUMB void OverlayManager::Load(OverlaySlot index, OverlayId id) {
-    if (id != OverlayId_None) {
-        FS_LoadOverlay(NULL, data_0203e0e8[id]);
+THUMB void OverlayManager::Load(OverlaySlot slot, OverlayIndex index) {
+    if (index != OverlayIndex_None) {
+        FS_LoadOverlay(NULL, data_0203e0e8[index]);
     }
 
-    gOverlayManager.mLoadedOverlays[index] = id;
+    gOverlayManager.mLoadedOverlays[slot] = index;
 }
 
-THUMB void OverlayManager::Unload(OverlaySlot index) {
+THUMB void OverlayManager::Unload(OverlaySlot slot) {
     OverlayManager* pOverlayManager = &gOverlayManager;
 
-    if (pOverlayManager->mLoadedOverlays[index] != OverlayId_None) {
-        FS_UnloadOverlay(NULL, data_0203e0e8[pOverlayManager->mLoadedOverlays[index]]);
-        pOverlayManager->mLoadedOverlays[index] = OverlayId_None;
+    if (pOverlayManager->mLoadedOverlays[slot] != OverlayIndex_None) {
+        FS_UnloadOverlay(NULL, data_0203e0e8[pOverlayManager->mLoadedOverlays[slot]]);
+        pOverlayManager->mLoadedOverlays[slot] = OverlayIndex_None;
     }
 }