diff --git a/clang/include/clang/Basic/Builtins.def b/clang/include/clang/Basic/Builtins.def
index c060d49ba338..1416a64543a4 100644
--- a/clang/include/clang/Basic/Builtins.def
+++ b/clang/include/clang/Basic/Builtins.def
@@ -65,6 +65,7 @@
 // & -> reference (optionally followed by an address space number)
 // C -> const
 // D -> volatile
+// R -> restrict
 
 // The third value provided to the macro specifies information about attributes
 // of the function.  These must be kept in sync with the predicates in the