diff --git a/lib/Support/StringRef.cpp b/lib/Support/StringRef.cpp
index 40b732c62db..c33ca6a2ebf 100644
--- a/lib/Support/StringRef.cpp
+++ b/lib/Support/StringRef.cpp
@@ -31,14 +31,14 @@ static bool ascii_isdigit(char x) {
 /// compare_lower - Compare strings, ignoring case.
 int StringRef::compare_lower(StringRef RHS) const {
   for (size_t I = 0, E = min(Length, RHS.Length); I != E; ++I) {
-    char LHC = ascii_tolower(Data[I]);
-    char RHC = ascii_tolower(RHS.Data[I]);
+    unsigned char LHC = ascii_tolower(Data[I]);
+    unsigned char RHC = ascii_tolower(RHS.Data[I]);
     if (LHC != RHC)
       return LHC < RHC ? -1 : 1;
   }
 
   if (Length == RHS.Length)
-        return 0;
+    return 0;
   return Length < RHS.Length ? -1 : 1;
 }
 
@@ -62,7 +62,7 @@ int StringRef::compare_numeric(StringRef RHS) const {
     return Data[I] < RHS.Data[I] ? -1 : 1;
   }
   if (Length == RHS.Length)
-        return 0;
+    return 0;
   return Length < RHS.Length ? -1 : 1;
 }
 
diff --git a/unittests/ADT/StringRefTest.cpp b/unittests/ADT/StringRefTest.cpp
index 887ba5d1f9e..de5c349cd60 100644
--- a/unittests/ADT/StringRefTest.cpp
+++ b/unittests/ADT/StringRefTest.cpp
@@ -53,6 +53,14 @@ TEST(StringRefTest, StringOps) {
   EXPECT_EQ( 1, StringRef("aab").compare("aaa"));
   EXPECT_EQ(-1, StringRef("aab").compare("aabb"));
   EXPECT_EQ( 1, StringRef("aab").compare("aa"));
+  EXPECT_EQ( 1, StringRef("\xFF").compare("\1"));
+
+  EXPECT_EQ(-1, StringRef("AaB").compare_lower("aAd"));
+  EXPECT_EQ( 0, StringRef("AaB").compare_lower("aab"));
+  EXPECT_EQ( 1, StringRef("AaB").compare_lower("AAA"));
+  EXPECT_EQ(-1, StringRef("AaB").compare_lower("aaBb"));
+  EXPECT_EQ( 1, StringRef("AaB").compare_lower("aA"));
+  EXPECT_EQ( 1, StringRef("\xFF").compare_lower("\1"));
 
   EXPECT_EQ(-1, StringRef("aab").compare_numeric("aad"));
   EXPECT_EQ( 0, StringRef("aab").compare_numeric("aab"));