diff --git a/lib/ClangImporter/ClangAdapter.cpp b/lib/ClangImporter/ClangAdapter.cpp
index 2a0bd7a19889b..9fa086d3a2e52 100644
--- a/lib/ClangImporter/ClangAdapter.cpp
+++ b/lib/ClangImporter/ClangAdapter.cpp
@@ -563,6 +563,8 @@ OptionalTypeKind importer::translateNullability(clang::NullabilityKind kind) {
   case clang::NullabilityKind::Unspecified:
     return OptionalTypeKind::OTK_ImplicitlyUnwrappedOptional;
   }
+
+  llvm_unreachable("Invalid NullabilityKind.");
 }
 
 bool importer::hasDesignatedInitializers(
diff --git a/lib/ClangImporter/ImportDecl.cpp b/lib/ClangImporter/ImportDecl.cpp
index bf32910cf9f55..898fdca6bb5d6 100644
--- a/lib/ClangImporter/ImportDecl.cpp
+++ b/lib/ClangImporter/ImportDecl.cpp
@@ -2739,6 +2739,8 @@ namespace {
         return nullptr;
       }
       }
+      
+      llvm_unreachable("Invalid EnumKind.");
     }
 
 
diff --git a/lib/ClangImporter/ImportEnumInfo.cpp b/lib/ClangImporter/ImportEnumInfo.cpp
index 685681cca7024..453583233eab2 100644
--- a/lib/ClangImporter/ImportEnumInfo.cpp
+++ b/lib/ClangImporter/ImportEnumInfo.cpp
@@ -222,6 +222,8 @@ void EnumInfo::determineConstantNamePrefix(ASTContext &ctx,
     case clang::AR_Unavailable:
       return false;
     }
+
+    llvm_unreachable("Invalid AvailabilityAttr.");
   };
 
   // Move to the first non-deprecated enumerator, or non-swift_name'd
diff --git a/lib/ClangImporter/ImportName.cpp b/lib/ClangImporter/ImportName.cpp
index e31d7e04f152b..7288d8cae5f68 100644
--- a/lib/ClangImporter/ImportName.cpp
+++ b/lib/ClangImporter/ImportName.cpp
@@ -1094,7 +1094,7 @@ ImportedName NameImporter::importNameImpl(const clang::NamedDecl *D,
   // Objective-C categories and extensions don't have names, despite
   // being "named" declarations.
   if (isa<clang::ObjCCategoryDecl>(D))
-    return {};
+    return ImportedName();
 
   // Dig out the definition, if there is one.
   if (auto def = getDefinitionForClangTypeDecl(D)) {
@@ -1106,7 +1106,7 @@ ImportedName NameImporter::importNameImpl(const clang::NamedDecl *D,
   auto dc = const_cast<clang::DeclContext *>(D->getDeclContext());
   auto effectiveCtx = determineEffectiveContext(D, dc, options);
   if (!effectiveCtx)
-    return {};
+    return ImportedName();
   result.EffectiveContext = effectiveCtx;
 
   // FIXME: ugly to check here, instead perform unified check up front in
@@ -1192,7 +1192,7 @@ ImportedName NameImporter::importNameImpl(const clang::NamedDecl *D,
         if (!shouldImportAsInitializer(method, initPrefixLength,
                                        result.InitKind)) {
           // We cannot import this as an initializer anyway.
-          return {};
+          return ImportedName();
         }
 
         // If this swift_name attribute maps a factory method to an
diff --git a/lib/ClangImporter/ImportName.h b/lib/ClangImporter/ImportName.h
index 0323ac1ec61c4..ab3958358e77d 100644
--- a/lib/ClangImporter/ImportName.h
+++ b/lib/ClangImporter/ImportName.h
@@ -130,6 +130,8 @@ struct ImportedName {
     case ImportedAccessorKind::SubscriptSetter:
       return true;
     }
+    
+    llvm_unreachable("Invalid ImportedAccessorKind.");
   }
 };
 
diff --git a/lib/ClangImporter/ImportType.cpp b/lib/ClangImporter/ImportType.cpp
index 4bdd187c595bf..95537e091fb42 100644
--- a/lib/ClangImporter/ImportType.cpp
+++ b/lib/ClangImporter/ImportType.cpp
@@ -140,6 +140,8 @@ namespace {
     case ImportHint::SwiftNewtypeFromCFPointer:
       return true;
     }
+
+    llvm_unreachable("Invalid ImportHint.");
   }
 
   struct ImportResult {
@@ -173,6 +175,8 @@ namespace {
         return OptionalType::get(payloadType);
       return ImplicitlyUnwrappedOptionalType::get(payloadType);
     }
+
+    llvm_unreachable("Invalid OptionalTypeKind.");
   }
 
   class SwiftTypeConverter :
@@ -296,6 +300,8 @@ namespace {
       case clang::BuiltinType::OMPArraySection:
         return Type();
       }
+
+      llvm_unreachable("Invalid BuiltinType.");
     }
 
     ImportResult VisitComplexType(const clang::ComplexType *type) {
@@ -783,6 +789,8 @@ namespace {
         return getAdjustedTypeDeclReferenceType(decl);
       }
       }
+
+      llvm_unreachable("Invalid EnumKind.");
     }
 
     ImportResult VisitObjCObjectType(const clang::ObjCObjectType *type) {
@@ -1051,6 +1059,8 @@ static bool canBridgeTypes(ImportTypeKind importKind) {
   case ImportTypeKind::BridgedValue:
     return true;
   }
+
+  llvm_unreachable("Invalid ImportTypeKind.");
 }
 
 /// True if the type has known CoreFoundation reference counting semantics.
@@ -1075,6 +1085,8 @@ static bool isCFAudited(ImportTypeKind importKind) {
   case ImportTypeKind::PropertyWithReferenceSemantics:
     return true;
   }
+
+  llvm_unreachable("Invalid ImportTypeKind.");
 }
 
 /// Turn T into Unmanaged<T>.
@@ -1744,6 +1756,8 @@ adjustResultTypeForThrowingFunction(const ImportedErrorInfo &errorInfo,
   case ForeignErrorConvention::NonNilError:
     return resultTy;
   }
+
+  llvm_unreachable("Invalid ForeignErrorConvention.");
 }
                                      
 /// Produce the foreign error convention from the imported error info,
diff --git a/lib/ClangImporter/SwiftLookupTable.cpp b/lib/ClangImporter/SwiftLookupTable.cpp
index 86eacd6a19ce9..3d2b98bd93817 100644
--- a/lib/ClangImporter/SwiftLookupTable.cpp
+++ b/lib/ClangImporter/SwiftLookupTable.cpp
@@ -214,6 +214,8 @@ bool SwiftLookupTable::contextRequiresName(ContextKind kind) {
   case ContextKind::TranslationUnit:
     return false;
   }
+
+  llvm_unreachable("Invalid ContextKind.");
 }
 
 /// Try to translate the given Clang declaration into a context.
@@ -293,6 +295,8 @@ SwiftLookupTable::translateContext(EffectiveClangContext context) {
 
     return None;
   }
+
+  llvm_unreachable("Invalid EffectiveClangContext.");
 }
 
 /// Lookup an unresolved context name and resolve it to a Clang