diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 192862d..8a87b9f 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -559,6 +559,10 @@
     Builder.defineMacro("__cpp_experimental_concepts", "1");
   if (LangOpts.CoroutinesTS)
     Builder.defineMacro("__cpp_coroutines", "201703L");
+
+  // Potential future breaking changes.
+  if (LangOpts.Char8)
+    Builder.defineMacro("__cpp_char8_t", "201803");
 }
 
 static void InitializePredefinedMacros(const TargetInfo &TI,
@@ -939,6 +943,8 @@
                                        InlineWidthBits));
     DEFINE_LOCK_FREE_MACRO(BOOL, Bool);
     DEFINE_LOCK_FREE_MACRO(CHAR, Char);
+    if (LangOpts.Char8)
+      DEFINE_LOCK_FREE_MACRO(CHAR8_T, Char); // Treat char8_t like char.
     DEFINE_LOCK_FREE_MACRO(CHAR16_T, Char16);
     DEFINE_LOCK_FREE_MACRO(CHAR32_T, Char32);
     DEFINE_LOCK_FREE_MACRO(WCHAR_T, WChar);