diff --git a/googletest/src/gtest.cc b/googletest/src/gtest.cc
index 7c5b6af9..a74041e7 100644
--- a/googletest/src/gtest.cc
+++ b/googletest/src/gtest.cc
@@ -1949,8 +1949,8 @@ bool String::CaseInsensitiveWideCStringEquals(const wchar_t* lhs,
   // Other unknown OSes may not define it either.
   wint_t left, right;
   do {
-    left = towlower(*lhs++);
-    right = towlower(*rhs++);
+    left = towlower(static_cast<wint_t>(*lhs++));
+    right = towlower(static_cast<wint_t>(*rhs++));
   } while (left && left == right);
   return left == right;
 #endif  // OS selector