diff --git a/HACKING b/HACKING
index 9ae20a6f0..df28b7aff 100644
--- a/HACKING
+++ b/HACKING
@@ -120,6 +120,9 @@ m4/
 ocaml/
         OCaml bindings.
 
+php/
+        PHP bindings.
+
 po/
         Translations of simple gettext strings.  For translations of
         longer documents, see po-docs/.