diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index bf289c1..995191a 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -63,7 +63,7 @@
  */
 typedef struct hb_glyph_info_t {
   hb_codepoint_t codepoint;
-  hb_mask_t      mask;
+  hb_mask_t      mask; /* Holds hb_glyph_flags_t after hb_shape() */
   uint32_t       cluster;
 
   /*< private >*/
@@ -71,6 +71,11 @@
   hb_var_int_t   var2;
 } hb_glyph_info_t;
 
+typedef enum { /*< flags >*/
+  HB_GLYPH_FLAG_UNSAFE_TO_BREAK		= 0x00000002,
+  HB_GLYPH_FLAG_DEFINED			= 0x00000002 /* OR of all defined flags */
+} hb_glyph_flags_t;
+
 /**
  * hb_glyph_position_t:
  * @x_advance: how much the line advances after drawing this glyph when setting
@@ -403,7 +408,8 @@
   HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS		= 0x00000001u,
   HB_BUFFER_SERIALIZE_FLAG_NO_POSITIONS		= 0x00000002u,
   HB_BUFFER_SERIALIZE_FLAG_NO_GLYPH_NAMES	= 0x00000004u,
-  HB_BUFFER_SERIALIZE_FLAG_GLYPH_EXTENTS	= 0x00000008u
+  HB_BUFFER_SERIALIZE_FLAG_GLYPH_EXTENTS	= 0x00000008u,
+  HB_BUFFER_SERIALIZE_FLAG_GLYPH_FLAGS		= 0x00000010u
 } hb_buffer_serialize_flags_t;
 
 /**