diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index dbb59b4..d4943e7 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -315,10 +315,13 @@
     else if (!LangOpts.GNUMode && LangOpts.Digraphs)
       Builder.defineMacro("__STDC_VERSION__", "199409L");
   } else {
+    // FIXME: Use correct value for C++17.
+    if (LangOpts.CPlusPlus1z)
+      Builder.defineMacro("__cplusplus", "201406L");
     // C++1y [cpp.predefined]p1:
     //   The name __cplusplus is defined to the value 201402L when compiling a
     //   C++ translation unit.
-     if (LangOpts.CPlusPlus1y)
+    else if (LangOpts.CPlusPlus1y)
       Builder.defineMacro("__cplusplus", "201402L");
     // C++11 [cpp.predefined]p1:
     //   The name __cplusplus is defined to the value 201103L when compiling a