diff --git a/src/hb.hh b/src/hb.hh
index 67f09b981..ec24c1ae0 100644
--- a/src/hb.hh
+++ b/src/hb.hh
@@ -214,6 +214,7 @@ extern "C" int hb_memalign_impl(void **memptr, size_t alignment, size_t size);
  * Compiler attributes
  */
 
+/* https://github.com/harfbuzz/harfbuzz/issues/1634 */
 #if __cplusplus < 201103L && !defined(_MSC_VER)
 
 #ifndef nullptr