diff --git a/lib/Support/StringRef.cpp b/lib/Support/StringRef.cpp
index c78b6d0..e73c6e3 100644
--- a/lib/Support/StringRef.cpp
+++ b/lib/Support/StringRef.cpp
@@ -152,7 +152,7 @@
 std::string StringRef::upper() const {
   std::string Result(size(), char());
   for (size_type i = 0, e = size(); i != e; ++i) {
-    Result[i] = ascii_tolower(Data[i]);
+    Result[i] = ascii_toupper(Data[i]);
   }
   return Result;
 }