diff --git a/include/llvm/ADT/StringRef.h b/include/llvm/ADT/StringRef.h
index f1861c8f92b..778fa10a32c 100644
--- a/include/llvm/ADT/StringRef.h
+++ b/include/llvm/ADT/StringRef.h
@@ -347,8 +347,11 @@ namespace llvm {
     typename std::enable_if<!std::numeric_limits<T>::is_signed, bool>::type
     getAsInteger(unsigned Radix, T &Result) const {
       unsigned long long ULLVal;
+      // The additional cast to unsigned long long is required to avoid the
+      // Visual C++ warning C4805: '!=' : unsafe mix of type 'bool' and type
+      // 'unsigned __int64' when instantiating getAsInteger with T = bool.
       if (getAsUnsignedInteger(*this, Radix, ULLVal) ||
-            static_cast<T>(ULLVal) != ULLVal)
+          static_cast<unsigned long long>(static_cast<T>(ULLVal)) != ULLVal)
         return true;
       Result = ULLVal;
       return false;