diff --git a/llvm/include/llvm/BinaryFormat/COFF.h b/llvm/include/llvm/BinaryFormat/COFF.h
index 72461d0d9c316..4c31cd847bdfb 100644
--- a/llvm/include/llvm/BinaryFormat/COFF.h
+++ b/llvm/include/llvm/BinaryFormat/COFF.h
@@ -806,6 +806,12 @@ enum Feat00Flags : uint32_t {
   Kernel = 0x40000000,
 };
 
+enum class Arm64ECThunkType : uint8_t {
+  GuestExit = 0,
+  Entry = 1,
+  Exit = 4,
+};
+
 inline bool isReservedSectionNumber(int32_t SectionNumber) {
   return SectionNumber <= 0;
 }
diff --git a/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp b/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp
index f147ded2ab701..9b5cbe3de137b 100644
--- a/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp
@@ -30,6 +30,7 @@
 #include "llvm/TargetParser/Triple.h"
 
 using namespace llvm;
+using namespace llvm::COFF;
 using namespace llvm::object;
 
 using OperandBundleDef = OperandBundleDefT<Value *>;
@@ -45,8 +46,6 @@ static cl::opt<bool> GenerateThunks("arm64ec-generate-thunks", cl::Hidden,
 
 namespace {
 
-enum class ThunkType { GuestExit, Entry, Exit };
-
 class AArch64Arm64ECCallLowering : public ModulePass {
 public:
   static char ID;
@@ -73,15 +72,15 @@ class AArch64Arm64ECCallLowering : public ModulePass {
   Type *I64Ty;
   Type *VoidTy;
 
-  void getThunkType(FunctionType *FT, AttributeList AttrList, ThunkType TT,
-                    raw_ostream &Out, FunctionType *&Arm64Ty,
-                    FunctionType *&X64Ty);
+  void getThunkType(FunctionType *FT, AttributeList AttrList,
+                    Arm64ECThunkType TT, raw_ostream &Out,
+                    FunctionType *&Arm64Ty, FunctionType *&X64Ty);
   void getThunkRetType(FunctionType *FT, AttributeList AttrList,
                        raw_ostream &Out, Type *&Arm64RetTy, Type *&X64RetTy,
                        SmallVectorImpl<Type *> &Arm64ArgTypes,
                        SmallVectorImpl<Type *> &X64ArgTypes, bool &HasSretPtr);
-  void getThunkArgTypes(FunctionType *FT, AttributeList AttrList, ThunkType TT,
-                        raw_ostream &Out,
+  void getThunkArgTypes(FunctionType *FT, AttributeList AttrList,
+                        Arm64ECThunkType TT, raw_ostream &Out,
                         SmallVectorImpl<Type *> &Arm64ArgTypes,
                         SmallVectorImpl<Type *> &X64ArgTypes, bool HasSretPtr);
   void canonicalizeThunkType(Type *T, Align Alignment, bool Ret,
@@ -91,13 +90,11 @@ class AArch64Arm64ECCallLowering : public ModulePass {
 
 } // end anonymous namespace
 
-void AArch64Arm64ECCallLowering::getThunkType(FunctionType *FT,
-                                              AttributeList AttrList,
-                                              ThunkType TT, raw_ostream &Out,
-                                              FunctionType *&Arm64Ty,
-                                              FunctionType *&X64Ty) {
-  Out << (TT == ThunkType::Entry ? "$ientry_thunk$cdecl$"
-                                 : "$iexit_thunk$cdecl$");
+void AArch64Arm64ECCallLowering::getThunkType(
+    FunctionType *FT, AttributeList AttrList, Arm64ECThunkType TT,
+    raw_ostream &Out, FunctionType *&Arm64Ty, FunctionType *&X64Ty) {
+  Out << (TT == Arm64ECThunkType::Entry ? "$ientry_thunk$cdecl$"
+                                        : "$iexit_thunk$cdecl$");
 
   Type *Arm64RetTy;
   Type *X64RetTy;
@@ -108,7 +105,7 @@ void AArch64Arm64ECCallLowering::getThunkType(FunctionType *FT,
   // The first argument to a thunk is the called function, stored in x9.
   // For exit thunks, we pass the called function down to the emulator;
   // for entry/guest exit thunks, we just call the Arm64 function directly.
-  if (TT == ThunkType::Exit)
+  if (TT == Arm64ECThunkType::Exit)
     Arm64ArgTypes.push_back(PtrTy);
   X64ArgTypes.push_back(PtrTy);
 
@@ -125,8 +122,8 @@ void AArch64Arm64ECCallLowering::getThunkType(FunctionType *FT,
 }
 
 void AArch64Arm64ECCallLowering::getThunkArgTypes(
-    FunctionType *FT, AttributeList AttrList, ThunkType TT, raw_ostream &Out,
-    SmallVectorImpl<Type *> &Arm64ArgTypes,
+    FunctionType *FT, AttributeList AttrList, Arm64ECThunkType TT,
+    raw_ostream &Out, SmallVectorImpl<Type *> &Arm64ArgTypes,
     SmallVectorImpl<Type *> &X64ArgTypes, bool HasSretPtr) {
 
   Out << "$";
@@ -163,7 +160,7 @@ void AArch64Arm64ECCallLowering::getThunkArgTypes(
     X64ArgTypes.push_back(PtrTy);
     // x5
     Arm64ArgTypes.push_back(I64Ty);
-    if (TT != ThunkType::Entry) {
+    if (TT != Arm64ECThunkType::Entry) {
       // FIXME: x5 isn't actually used by the x64 side; revisit once we
       // have proper isel for varargs
       X64ArgTypes.push_back(I64Ty);
@@ -348,7 +345,8 @@ Function *AArch64Arm64ECCallLowering::buildExitThunk(FunctionType *FT,
   SmallString<256> ExitThunkName;
   llvm::raw_svector_ostream ExitThunkStream(ExitThunkName);
   FunctionType *Arm64Ty, *X64Ty;
-  getThunkType(FT, Attrs, ThunkType::Exit, ExitThunkStream, Arm64Ty, X64Ty);
+  getThunkType(FT, Attrs, Arm64ECThunkType::Exit, ExitThunkStream, Arm64Ty,
+               X64Ty);
   if (Function *F = M->getFunction(ExitThunkName))
     return F;
 
@@ -451,8 +449,8 @@ Function *AArch64Arm64ECCallLowering::buildEntryThunk(Function *F) {
   SmallString<256> EntryThunkName;
   llvm::raw_svector_ostream EntryThunkStream(EntryThunkName);
   FunctionType *Arm64Ty, *X64Ty;
-  getThunkType(F->getFunctionType(), F->getAttributes(), ThunkType::Entry,
-               EntryThunkStream, Arm64Ty, X64Ty);
+  getThunkType(F->getFunctionType(), F->getAttributes(),
+               Arm64ECThunkType::Entry, EntryThunkStream, Arm64Ty, X64Ty);
   if (Function *F = M->getFunction(EntryThunkName))
     return F;
 
@@ -543,8 +541,8 @@ Function *AArch64Arm64ECCallLowering::buildEntryThunk(Function *F) {
 Function *AArch64Arm64ECCallLowering::buildGuestExitThunk(Function *F) {
   llvm::raw_null_ostream NullThunkName;
   FunctionType *Arm64Ty, *X64Ty;
-  getThunkType(F->getFunctionType(), F->getAttributes(), ThunkType::GuestExit,
-               NullThunkName, Arm64Ty, X64Ty);
+  getThunkType(F->getFunctionType(), F->getAttributes(),
+               Arm64ECThunkType::GuestExit, NullThunkName, Arm64Ty, X64Ty);
   auto MangledName = getArm64ECMangledFunctionName(F->getName().str());
   assert(MangledName && "Can't guest exit to function that's already native");
   std::string ThunkName = *MangledName;
@@ -679,7 +677,7 @@ bool AArch64Arm64ECCallLowering::runOnModule(Module &Mod) {
   struct ThunkInfo {
     Constant *Src;
     Constant *Dst;
-    unsigned Kind;
+    Arm64ECThunkType Kind;
   };
   SmallVector<ThunkInfo> ThunkMapping;
   for (Function &F : Mod) {
@@ -688,14 +686,17 @@ bool AArch64Arm64ECCallLowering::runOnModule(Module &Mod) {
         F.getCallingConv() != CallingConv::ARM64EC_Thunk_X64) {
       if (!F.hasComdat())
         F.setComdat(Mod.getOrInsertComdat(F.getName()));
-      ThunkMapping.push_back({&F, buildEntryThunk(&F), 1});
+      ThunkMapping.push_back(
+          {&F, buildEntryThunk(&F), Arm64ECThunkType::Entry});
     }
   }
   for (Function *F : DirectCalledFns) {
     ThunkMapping.push_back(
-        {F, buildExitThunk(F->getFunctionType(), F->getAttributes()), 4});
+        {F, buildExitThunk(F->getFunctionType(), F->getAttributes()),
+         Arm64ECThunkType::Exit});
     if (!F->hasDLLImportStorageClass())
-      ThunkMapping.push_back({buildGuestExitThunk(F), F, 0});
+      ThunkMapping.push_back(
+          {buildGuestExitThunk(F), F, Arm64ECThunkType::GuestExit});
   }
 
   if (!ThunkMapping.empty()) {
@@ -704,7 +705,7 @@ bool AArch64Arm64ECCallLowering::runOnModule(Module &Mod) {
       ThunkMappingArrayElems.push_back(ConstantStruct::getAnon(
           {ConstantExpr::getBitCast(Thunk.Src, PtrTy),
            ConstantExpr::getBitCast(Thunk.Dst, PtrTy),
-           ConstantInt::get(M->getContext(), APInt(32, Thunk.Kind))}));
+           ConstantInt::get(M->getContext(), APInt(32, uint8_t(Thunk.Kind)))}));
     }
     Constant *ThunkMappingArray = ConstantArray::get(
         llvm::ArrayType::get(ThunkMappingArrayElems[0]->getType(),