diff --git a/clang-tools-extra/clang-tidy/utils/HeaderFileExtensionsUtils.h b/clang-tools-extra/clang-tidy/utils/HeaderFileExtensionsUtils.h
--- a/clang-tools-extra/clang-tidy/utils/HeaderFileExtensionsUtils.h
+++ b/clang-tools-extra/clang-tidy/utils/HeaderFileExtensionsUtils.h
@@ -18,7 +18,7 @@
 namespace tidy {
 namespace utils {
 
-typedef llvm::SmallSet<llvm::StringRef, 5> HeaderFileExtensionsSet;
+using HeaderFileExtensionsSet = SmallSet<StringRef, 5>;
 
 /// \brief Checks whether expansion location of \p Loc is in header file.
 bool isExpansionLocInHeaderFile(
diff --git a/clang/include/clang/Basic/LLVM.h b/clang/include/clang/Basic/LLVM.h
--- a/clang/include/clang/Basic/LLVM.h
+++ b/clang/include/clang/Basic/LLVM.h
@@ -31,6 +31,7 @@
   template<typename T> class ArrayRef;
   template<typename T> class MutableArrayRef;
   template<typename T> class OwningArrayRef;
+  template<typename T, unsigned N, typename C> class SmallSet;
   template<unsigned InternalLen> class SmallString;
   template<typename T, unsigned N> class SmallVector;
   template<typename T> class SmallVectorImpl;
@@ -66,6 +67,7 @@
   using llvm::Optional;
   using llvm::OwningArrayRef;
   using llvm::SaveAndRestore;
+  using llvm::SmallSet;
   using llvm::SmallString;
   using llvm::SmallVector;
   using llvm::SmallVectorImpl;