diff --git a/clang/Sema/SemaChecking.cpp b/clang/Sema/SemaChecking.cpp
index fe82ea6b85fc..6d3eea5e730b 100644
--- a/clang/Sema/SemaChecking.cpp
+++ b/clang/Sema/SemaChecking.cpp
@@ -244,6 +244,9 @@ bool Sema::SemaBuiltinUnorderedCompare(CallExpr *TheCall) {
 ///
 ///  (8) Check that the format string is a wide literal.
 ///
+///  (9) Also check the arguments of functions with the __format__ attribute.
+///      (TODO).
+///
 /// All of these checks can be done by parsing the format string.
 ///
 /// For now, we ONLY do (1), (3), (5), (6), (7), and (8).