diff --git a/src/hb-set.hh b/src/hb-set.hh
index 2f776da69..ad449d0ce 100644
--- a/src/hb-set.hh
+++ b/src/hb-set.hh
@@ -28,6 +28,7 @@
 #define HB_SET_HH
 
 #include "hb.hh"
+#include "hb-machinery.hh"
 
 
 /*