diff --git a/include/Support/StringExtras.h b/include/Support/StringExtras.h
index daf866f301d..ce268caa5e1 100644
--- a/include/Support/StringExtras.h
+++ b/include/Support/StringExtras.h
@@ -97,11 +97,11 @@ static inline std::string ftostr(double V) {
   return Buffer;
 }
 
-static inline std::string LowercaseString (const std::string &S) { 
+static inline std::string LowercaseString(const std::string &S) { 
   std::string result (S);
   for (unsigned i = 0; i < S.length(); ++i)
     if (isupper (result[i]))
-      result[i] = tolower(result[i]);
+      result[i] = (char)tolower(result[i]);
   return result;
 }
 
diff --git a/include/llvm/ADT/StringExtras.h b/include/llvm/ADT/StringExtras.h
index daf866f301d..ce268caa5e1 100644
--- a/include/llvm/ADT/StringExtras.h
+++ b/include/llvm/ADT/StringExtras.h
@@ -97,11 +97,11 @@ static inline std::string ftostr(double V) {
   return Buffer;
 }
 
-static inline std::string LowercaseString (const std::string &S) { 
+static inline std::string LowercaseString(const std::string &S) { 
   std::string result (S);
   for (unsigned i = 0; i < S.length(); ++i)
     if (isupper (result[i]))
-      result[i] = tolower(result[i]);
+      result[i] = (char)tolower(result[i]);
   return result;
 }