diff --git a/src/Makefile.sources b/src/Makefile.sources
index 5e1c4e4f6c6f5dd2b6fd113b53e11320d0c055bc..0d5af32439331252e98c256747246415b7e11216 100644
--- a/src/Makefile.sources
+++ b/src/Makefile.sources
@@ -189,7 +189,7 @@ HB_SUBSET_sources = \
 
 HB_SUBSET_headers = \
 	hb-subset.h \
-	hb-subset-plan.h \
+	hb-subset-plan.hh \
 	hb-subset-private.hh \
 	$(NULL)
 
diff --git a/src/hb-subset-plan.cc b/src/hb-subset-plan.cc
index 7da9dae8f2e7f6262280773ae05387e06e3d42a5..8111d519b479ab1e3f5a89d13ad2da357ea7e925 100644
--- a/src/hb-subset-plan.cc
+++ b/src/hb-subset-plan.cc
@@ -24,15 +24,15 @@
  * Google Author(s): Garret Rieger
  */
 
-#include "hb-private.hh"
+#include "hb-subset-plan.hh"
+#include "hb-subset-private.hh"
 
-#include "hb-object-private.hh"
-
-
-struct hb_subset_plan_t {
-  hb_object_header_t header;
-  ASSERT_POD ();
-};
+hb_set_t *
+get_glyph_ids_from_cmap (hb_face_t *face,
+                         hb_set_t  *codepoints)
+{
+  return hb_set_get_empty ();
+}
 
 /**
  * hb_subset_plan_create:
@@ -49,13 +49,17 @@ hb_subset_plan_create (hb_face_t           *face,
                        hb_subset_profile_t *profile,
                        hb_subset_input_t   *input)
 {
-  return hb_object_create<hb_subset_plan_t>();
+  hb_subset_plan_t *plan = hb_object_create<hb_subset_plan_t> ();
+  plan->glyphs_to_retain = get_glyph_ids_from_cmap (face, input->codepoints);
+  return plan;
 }
 
 hb_subset_plan_t *
-hb_subset_plan_create_empty ()
+hb_subset_plan_get_empty ()
 {
-  return hb_object_create<hb_subset_plan_t>();
+  hb_subset_plan_t *plan = hb_object_create<hb_subset_plan_t> ();
+  plan->glyphs_to_retain = hb_set_get_empty();
+  return plan;
 }
 
 /**
@@ -68,5 +72,6 @@ hb_subset_plan_destroy (hb_subset_plan_t *plan)
 {
   if (!hb_object_destroy (plan)) return;
 
+  hb_set_destroy (plan->glyphs_to_retain);
   free (plan);
 }
diff --git a/src/hb-subset-plan.h b/src/hb-subset-plan.hh
similarity index 86%
rename from src/hb-subset-plan.h
rename to src/hb-subset-plan.hh
index 2fd46ae27fae12d9b80a445c5b080a1ae102f7e0..54b1e651dbe6f37067a6a035b13586f23e477bfb 100644
--- a/src/hb-subset-plan.h
+++ b/src/hb-subset-plan.hh
@@ -24,26 +24,30 @@
  * Google Author(s): Garret Rieger
  */
 
-#ifndef HB_H_IN
-#error "Include <hb.h> instead."
-#endif
-
 #ifndef HB_SUBSET_PLAN_H
 #define HB_SUBSET_PLAN_H
 
-HB_BEGIN_DECLS
+#include "hb-private.hh"
+#include "hb-object-private.hh"
+
+struct hb_subset_plan_t {
+  hb_object_header_t header;
+  ASSERT_POD ();
+
+  hb_set_t *glyphs_to_retain;
+};
 
 typedef struct hb_subset_plan_t hb_subset_plan_t;
 
-HB_EXTERN hb_subset_plan_t *
+hb_subset_plan_t *
 hb_subset_plan_create (hb_face_t           *face,
                        hb_subset_profile_t *profile,
                        hb_subset_input_t   *input);
 
-HB_EXTERN hb_subset_plan_t *
-hb_subset_plan_create_empty ();
+hb_subset_plan_t *
+hb_subset_plan_get_empty ();
 
-HB_EXTERN void
+void
 hb_subset_plan_destroy (hb_subset_plan_t *plan);
 
 #endif /* HB_SUBSET_PLAN_PRIVATE_HH */