diff --git a/src/graph/split-helpers.hh b/src/graph/split-helpers.hh
index 2fbffda07..61fd7c2d2 100644
--- a/src/graph/split-helpers.hh
+++ b/src/graph/split-helpers.hh
@@ -30,6 +30,7 @@
 namespace graph {
 
 template<typename Context>
+HB_INTERNAL
 hb_vector_t<unsigned> actuate_subtable_split (Context& split_context,
                                               const hb_vector_t<unsigned>& split_points)
 {