diff --git a/README b/README
index 336f9c5a9..40c8b09e2 100644
--- a/README
+++ b/README
@@ -973,6 +973,9 @@ links to link to the others, as described above.
 
 Unlike regular reference links, these references are case-sensitive.
 
+Note:  if you have defined an explicit identifier for a header,
+then implicit references to it will not work.
+
 Block quotations
 ----------------