diff --git a/unittests/ADT/TwineTest.cpp b/unittests/ADT/TwineTest.cpp
index dae5fa02a1a..2f874769507 100644
--- a/unittests/ADT/TwineTest.cpp
+++ b/unittests/ADT/TwineTest.cpp
@@ -36,7 +36,7 @@ TEST(TwineTest, Numbers) {
   EXPECT_EQ("123", Twine::utostr(123).str());
   EXPECT_EQ("-123", Twine::itostr(-123).str());
   EXPECT_EQ("123", Twine::utostr((char) 123).str());
-  EXPECT_EQ("-123", Twine::itostr((char) -123).str());
+  EXPECT_EQ("-123", Twine::itostr((signed char) -123).str());
 
   EXPECT_EQ("7B", Twine::utohexstr(123).str());
   EXPECT_EQ("FFFFFFFFFFFFFF85", Twine::itohexstr(-123).str());