diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index 520141b..4b285bb 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -185,7 +185,19 @@
 hb_buffer_flags_t
 hb_buffer_get_flags (hb_buffer_t *buffer);
 
+typedef enum {
+  HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES	= 0,
+  HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS	= 1,
+  HB_BUFFER_CLUSTER_LEVEL_CHARACTERS		= 2,
+  HB_BUFFER_CLUSTER_LEVEL_DEFAULT = HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES
+} hb_buffer_cluster_level_t;
 
+void
+hb_buffer_set_cluster_level (hb_buffer_t               *buffer,
+			     hb_buffer_cluster_level_t  cluster_level);
+
+hb_buffer_cluster_level_t
+hb_buffer_get_cluster_level (hb_buffer_t *buffer);
 
 #define HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT 0xFFFDu