diff --git a/include/llvm/ADT/StringSet.h b/include/llvm/ADT/StringSet.h
index 00048361e86..9c55f6b70e3 100644
--- a/include/llvm/ADT/StringSet.h
+++ b/include/llvm/ADT/StringSet.h
@@ -15,7 +15,6 @@
 #define LLVM_ADT_STRINGSET_H
 
 #include "llvm/ADT/StringMap.h"
-#include <cassert>
 
 namespace llvm {
 
@@ -26,10 +25,10 @@ namespace llvm {
   class StringSet : public llvm::StringMap<char, AllocatorTy> {
     typedef llvm::StringMap<char, AllocatorTy> base;
   public:
-    bool insert(const std::string& InLang) {
+    bool insert(StringRef InLang) {
       assert(!InLang.empty());
-      const char* KeyStart = &InLang[0];
-      const char* KeyEnd = KeyStart + InLang.size();
+      const char *KeyStart = InLang.data();
+      const char *KeyEnd = KeyStart + InLang.size();
       return base::insert(llvm::StringMapEntry<char>::
                           Create(KeyStart, KeyEnd, base::getAllocator(), '+'));
     }