diff --git a/src/hb-subset.h b/src/hb-subset.h
index 08e52dbd2..ee9187975 100644
--- a/src/hb-subset.h
+++ b/src/hb-subset.h
@@ -70,6 +70,17 @@ typedef struct hb_subset_plan_t hb_subset_plan_t;
  * in the final subset.
  * @HB_SUBSET_FLAGS_NO_PRUNE_UNICODE_RANGES: If set then the unicode ranges in
  * OS/2 will not be recalculated.
+ * @HB_SUBSET_FLAGS_ADD_ACCELERATOR_DATA: If set the subsetter will append into
+ * the output hb_face_t's user data, accelerator data that can be used to speedup
+ * further subsetting operations on the face.
+ * @HB_SUBSET_FLAGS_PATCH_MODE: If set the subsetter behaviour will be modified
+ * to produce a subset that is better suited to patching. For example cmap
+ * subtable format will be kept stable.
+ * @HB_SUBSET_FLAGS_OMIT_GLYF: If set the subsetter won't actually produce the final
+ * glyf table bytes. The table directory will include and entry as if the table was
+ * there but the actual final font blob will be truncated prior to the glyf data. This
+ * is a useful performance optimization when a font aware binary patching algorithm
+ * is being used to diff two subsets.
  *
  * List of boolean properties that can be configured on the subset input.
  *
@@ -86,6 +97,9 @@ typedef enum { /*< flags >*/
   HB_SUBSET_FLAGS_NOTDEF_OUTLINE =	     0x00000040u,
   HB_SUBSET_FLAGS_GLYPH_NAMES =		     0x00000080u,
   HB_SUBSET_FLAGS_NO_PRUNE_UNICODE_RANGES =  0x00000100u,
+  HB_SUBSET_FLAGS_ADD_ACCELERATOR_DATA =     0x00000200u,
+  HB_SUBSET_FLAGS_PATCH_MODE =               0x00000400u,
+  HB_SUBSET_FLAGS_OMIT_GLYF =                0x00000800u,
 } hb_subset_flags_t;
 
 /**