diff --git a/include/swift/Serialization/ModuleFile.h b/include/swift/Serialization/ModuleFile.h
index 93e812fda279a..0af74e92e2d17 100644
--- a/include/swift/Serialization/ModuleFile.h
+++ b/include/swift/Serialization/ModuleFile.h
@@ -142,7 +142,7 @@ class ModuleFile : public LazyMemberLoader {
   template <typename T>
   class Serialized {
   private:
-    using RawBitOffset = decltype(DeclTypeCursor.GetCurrentBitNo());
+    using RawBitOffset = uint64_t;
 
     using ImplTy = PointerUnion<T, serialization::BitOffset>;
     ImplTy Value;
@@ -310,7 +310,7 @@ class ModuleFile : public LazyMemberLoader {
   std::unique_ptr<GroupNameTable> GroupNamesMap;
   std::unique_ptr<SerializedDeclCommentTable> DeclCommentTable;
 
-  struct {
+  struct ModuleBits {
     /// The decl ID of the main class in this module file, if it has one.
     unsigned EntryPointDeclID : 31;
 
@@ -336,7 +336,7 @@ class ModuleFile : public LazyMemberLoader {
     // Explicitly pad out to the next word boundary.
     unsigned : 0;
   } Bits = {};
-  static_assert(sizeof(Bits) <= 8, "The bit set should be small");
+  static_assert(sizeof(ModuleBits) <= 8, "The bit set should be small");
 
   void setStatus(Status status) {
     Bits.Status = static_cast<unsigned>(status);
diff --git a/lib/Serialization/Deserialization.cpp b/lib/Serialization/Deserialization.cpp
index fba62f5bd36c2..d392ab189cb1a 100644
--- a/lib/Serialization/Deserialization.cpp
+++ b/lib/Serialization/Deserialization.cpp
@@ -57,6 +57,8 @@ namespace {
 #define RECORD(Id) case decls_block::Id: return #Id;
 #include "swift/Serialization/DeclTypeRecordNodes.def"
       }
+
+      llvm_unreachable("Unhandled RecordKind in switch.");
     }
 
     virtual void print(raw_ostream &os) const override {
@@ -4319,4 +4321,6 @@ Optional<ForeignErrorConvention> ModuleFile::maybeReadForeignErrorConvention() {
                                                   owned, replaced,
                                                   canErrorParameterType);
   }
+
+  llvm_unreachable("Unhandled ForeignErrorConvention in switch.");
 }
diff --git a/lib/Serialization/Serialization.cpp b/lib/Serialization/Serialization.cpp
index 5ac95e28b3330..5960fab7ae583 100644
--- a/lib/Serialization/Serialization.cpp
+++ b/lib/Serialization/Serialization.cpp
@@ -204,6 +204,8 @@ static const Decl *getDeclForContext(const DeclContext *DC) {
   case DeclContextKind::SubscriptDecl:
     return cast<SubscriptDecl>(DC);
   }
+
+  llvm_unreachable("Unhandled DeclContextKind in switch.");
 }
 
 namespace {
@@ -783,6 +785,8 @@ static uint8_t getRawStableDefaultArgumentKind(swift::DefaultArgumentKind kind)
   CASE(EmptyDictionary)
 #undef CASE
   }
+
+  llvm_unreachable("Unhandled DefaultArgumentKind in switch.");
 }
 
 static uint8_t getRawStableMetatypeRepresentation(AnyMetatypeType *metatype) {
@@ -934,6 +938,8 @@ static uint8_t getRawStableRequirementKind(RequirementKind kind) {
   CASE(SameType)
   }
 #undef CASE
+
+  llvm_unreachable("Unhandled RequirementKind in switch.");
 }
 
 void Serializer::writeGenericRequirements(ArrayRef<Requirement> requirements,
@@ -1283,6 +1289,8 @@ static uint8_t getRawStableOptionalTypeKind(swift::OptionalTypeKind kind) {
     return static_cast<uint8_t>(
              serialization::OptionalTypeKind::ImplicitlyUnwrappedOptional);
   }
+
+  llvm_unreachable("Unhandled OptionalTypeKind in switch.");
 }
 
 static bool shouldSerializeMember(Decl *D) {
@@ -1320,6 +1328,8 @@ static bool shouldSerializeMember(Decl *D) {
   case DeclKind::Func:
     return true;
   }
+
+  llvm_unreachable("Unhandled DeclKind in switch.");
 }
 
 void Serializer::writeMembers(DeclRange members, bool isClass) {
@@ -1386,6 +1396,8 @@ static serialization::AccessorKind getStableAccessorKind(swift::AccessorKind K){
   CASE(MutableAddressor)
 #undef CASE
   }
+
+  llvm_unreachable("Unhandled AccessorKind in switch.");
 }
 
 static serialization::CtorInitializerKind
@@ -1399,6 +1411,8 @@ getStableCtorInitializerKind(swift::CtorInitializerKind K){
       CASE(ConvenienceFactory)
 #undef CASE
   }
+
+  llvm_unreachable("Unhandled CtorInitializerKind in switch.");
 }
 
 void Serializer::writeCrossReference(const DeclContext *DC, uint32_t pathLen) {
@@ -1613,6 +1627,8 @@ static uint8_t getRawStableAssociativity(swift::Associativity assoc) {
   case swift::Associativity::None:
     return serialization::Associativity::NonAssociative;
   }
+
+  llvm_unreachable("Unhandled Associativity in switch.");
 }
 
 static serialization::StaticSpellingKind
@@ -1625,6 +1641,8 @@ getStableStaticSpelling(swift::StaticSpellingKind SS) {
   case swift::StaticSpellingKind::KeywordClass:
     return serialization::StaticSpellingKind::KeywordClass;
   }
+
+  llvm_unreachable("Unhandled StaticSpellingKind in switch.");
 }
 
 static uint8_t getRawStableAccessibility(Accessibility access) {
@@ -1639,6 +1657,8 @@ static uint8_t getRawStableAccessibility(Accessibility access) {
   CASE(Open)
 #undef CASE
   }
+
+  llvm_unreachable("Unhandled AccessibilityKind in switch.");
 }
 
 #ifndef NDEBUG
@@ -2029,6 +2049,8 @@ static ForeignErrorConventionKind getRawStableForeignErrorConventionKind(
   case ForeignErrorConvention::NonNilError:
     return ForeignErrorConventionKind::NonNilError;
   }
+
+  llvm_unreachable("Unhandled ForeignErrorConvention in switch.");
 }
 
 void Serializer::writeForeignErrorConvention(const ForeignErrorConvention &fec){