diff --git a/src/hb-ot-hmtx-table.hh b/src/hb-ot-hmtx-table.hh
index 36bffa70a..b667140e3 100644
--- a/src/hb-ot-hmtx-table.hh
+++ b/src/hb-ot-hmtx-table.hh
@@ -262,11 +262,10 @@ struct hmtxvmtx
     unsigned int num_advances_for_subset (const hb_subset_plan_t *plan) const
     {
       unsigned int num_advances = plan->num_output_glyphs ();
-      unsigned int last_advance = _advance_for_new_gid (plan,
-							num_advances - 1);
+      hb_codepoint_t old_gid = 0;
+      unsigned int last_advance = plan->old_gid_for_new_gid (num_advances - 1, &old_gid) ? get_advance (old_gid) : 0;
       while (num_advances > 1 &&
-	     last_advance == _advance_for_new_gid (plan,
-						   num_advances - 2))
+	     last_advance == (plan->old_gid_for_new_gid (num_advances - 2, &old_gid) ? get_advance (old_gid) : 0))
       {
 	num_advances--;
       }
@@ -274,17 +273,6 @@ struct hmtxvmtx
       return num_advances;
     }
 
-    private:
-    unsigned int _advance_for_new_gid (const hb_subset_plan_t *plan,
-				       hb_codepoint_t new_gid) const
-    {
-      hb_codepoint_t old_gid;
-      if (!plan->old_gid_for_new_gid (new_gid, &old_gid))
-	return 0;
-
-      return get_advance (old_gid);
-    }
-
     protected:
     unsigned int num_metrics;
     unsigned int num_advances;