diff --git a/lib/MC/SubtargetFeature.cpp b/lib/MC/SubtargetFeature.cpp
index f893104736a..fcb43d63cb9 100644
--- a/lib/MC/SubtargetFeature.cpp
+++ b/lib/MC/SubtargetFeature.cpp
@@ -85,7 +85,7 @@ void SubtargetFeatures::AddFeature(StringRef String) {
   // Don't add empty features.
   if (!String.empty())
     // Convert to lowercase, prepend flag if we don't already have a flag.
-    Features.push_back(hasFlag(String) ? String.str() : "+" + String.lower());
+    Features.push_back(hasFlag(String) ? String.lower() : "+" + String.lower());
 }
 
 /// Find KV in array using binary search.