diff --git a/include/clang/Rewrite/Core/Rewriter.h b/include/clang/Rewrite/Core/Rewriter.h
index f01e433f7fcce6cc0a066d59636d6518ba784fdf..2d2917b910b9414efa6f619393b678bb36377316 100644
--- a/include/clang/Rewrite/Core/Rewriter.h
+++ b/include/clang/Rewrite/Core/Rewriter.h
@@ -49,6 +49,9 @@ public:
 
   /// \brief Write to \p Stream the result of applying all changes to the
   /// original buffer.
+  /// Note that it isn't safe to use this function to overwrite memory mapped
+  /// files in-place (PR17960). Consider using a higher-level utility such as
+  /// Rewriter::overwriteChangedFiles() instead.
   ///
   /// The original buffer is not actually changed.
   raw_ostream &write(raw_ostream &Stream) const;