diff --git a/src/hb-buffer-verify.cc b/src/hb-buffer-verify.cc
index 345f08d26..76f821637 100644
--- a/src/hb-buffer-verify.cc
+++ b/src/hb-buffer-verify.cc
@@ -63,24 +63,25 @@ static bool
 buffer_verify_monotone (hb_buffer_t *buffer,
 			hb_font_t   *font)
 {
-  /* Check that clusters are monotone. */
-  if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES ||
-      buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS)
+  if (!HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE (buffer->cluster_level))
   {
-    bool is_forward = HB_DIRECTION_IS_FORWARD (hb_buffer_get_direction (buffer));
-
-    unsigned int num_glyphs;
-    hb_glyph_info_t *info = hb_buffer_get_glyph_infos (buffer, &num_glyphs);
-
-    for (unsigned int i = 1; i < num_glyphs; i++)
-      if (info[i-1].cluster != info[i].cluster &&
-	  (info[i-1].cluster < info[i].cluster) != is_forward)
-      {
-	buffer_verify_error (buffer, font, BUFFER_VERIFY_ERROR "clusters are not monotone.");
-	return false;
-      }
+    /* Cannot perform this check without monotone clusters. */
+    return true;
   }
 
+  bool is_forward = HB_DIRECTION_IS_FORWARD (hb_buffer_get_direction (buffer));
+
+  unsigned int num_glyphs;
+  hb_glyph_info_t *info = hb_buffer_get_glyph_infos (buffer, &num_glyphs);
+
+  for (unsigned int i = 1; i < num_glyphs; i++)
+    if (info[i-1].cluster != info[i].cluster &&
+	(info[i-1].cluster < info[i].cluster) != is_forward)
+    {
+      buffer_verify_error (buffer, font, BUFFER_VERIFY_ERROR "clusters are not monotone.");
+      return false;
+    }
+
   return true;
 }
 
@@ -92,8 +93,7 @@ buffer_verify_unsafe_to_break (hb_buffer_t  *buffer,
 			       unsigned int        num_features,
 			       const char * const *shapers)
 {
-  if (buffer->cluster_level != HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES &&
-      buffer->cluster_level != HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS)
+  if (!HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE (buffer->cluster_level))
   {
     /* Cannot perform this check without monotone clusters. */
     return true;
@@ -207,8 +207,7 @@ buffer_verify_unsafe_to_concat (hb_buffer_t        *buffer,
 				unsigned int        num_features,
 				const char * const *shapers)
 {
-  if (buffer->cluster_level != HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES &&
-      buffer->cluster_level != HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS)
+  if (!HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE (buffer->cluster_level))
   {
     /* Cannot perform this check without monotone clusters. */
     return true;
diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index d0c40664a..7fb95fe7e 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -518,7 +518,7 @@ void
 hb_buffer_t::merge_clusters_impl (unsigned int start,
 				  unsigned int end)
 {
-  if (cluster_level == HB_BUFFER_CLUSTER_LEVEL_CHARACTERS)
+  if (!HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE (cluster_level))
   {
     unsafe_to_break (start, end);
     return;
@@ -551,7 +551,7 @@ void
 hb_buffer_t::merge_out_clusters (unsigned int start,
 				 unsigned int end)
 {
-  if (cluster_level == HB_BUFFER_CLUSTER_LEVEL_CHARACTERS)
+  if (!HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE (cluster_level))
     return;
 
   if (unlikely (end - start < 2))
diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index dd0edb9b7..5d3b63f47 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -422,9 +422,9 @@ hb_buffer_get_flags (const hb_buffer_t *buffer);
  * @HB_BUFFER_CLUSTER_LEVEL_CHARACTERS: Don't group cluster values.
  * @HB_BUFFER_CLUSTER_LEVEL_DEFAULT: Default cluster level,
  *   equal to @HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES.
- * 
+ *
  * Data type for holding HarfBuzz's clustering behavior options. The cluster level
- * dictates one aspect of how HarfBuzz will treat non-base characters 
+ * dictates one aspect of how HarfBuzz will treat non-base characters
  * during shaping.
  *
  * In @HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES, non-base
@@ -446,9 +446,23 @@ 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_GRAPHEMES		= 3,
   HB_BUFFER_CLUSTER_LEVEL_DEFAULT = HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES
 } hb_buffer_cluster_level_t;
 
+#define HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE(level) \
+	((bool) ((1u << (unsigned) (level)) & \
+		 ((1u << HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES) | \
+		  (1u << HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS))))
+#define HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES(level) \
+	((bool) ((1u << (unsigned) (level)) & \
+		 ((1u << HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES) | \
+		  (1u << HB_BUFFER_CLUSTER_LEVEL_GRAPHEMES))))
+#define HB_BUFFER_CLUSTER_LEVEL_IS_CHARACTERS(level) \
+	((bool) ((1u << (unsigned) (level)) & \
+		 ((1u << HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARCATERS) | \
+		  (1u << HB_BUFFER_CLUSTER_LEVEL_CHARACTERS))))
+
 HB_EXTERN void
 hb_buffer_set_cluster_level (hb_buffer_t               *buffer,
 			     hb_buffer_cluster_level_t  cluster_level);
diff --git a/src/hb-coretext-shape.cc b/src/hb-coretext-shape.cc
index 0bb235f6d..2e029fe2b 100644
--- a/src/hb-coretext-shape.cc
+++ b/src/hb-coretext-shape.cc
@@ -646,7 +646,7 @@ _hb_coretext_shape (hb_shape_plan_t    *shape_plan,
    * B1 M1 B2 M2, and B1-B2 form a ligature, M2's cluster will
    * continue pointing to B2 even though B2 was merged into B1's
    * cluster... */
-  if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
+  if (HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES (buffer->cluster_level))
   {
     hb_unicode_funcs_t *unicode = buffer->unicode;
     unsigned int count = buffer->len;
@@ -1292,7 +1292,7 @@ resize_and_retry:
      * or the native OT backend, only that the cluster indices will be
      * monotonic in the output buffer. */
     if (count > 1 && (status_or & kCTRunStatusNonMonotonic) &&
-	buffer->cluster_level != HB_BUFFER_CLUSTER_LEVEL_CHARACTERS)
+	HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE (buffer->cluster_level))
     {
       hb_glyph_info_t *info = buffer->info;
       if (HB_DIRECTION_IS_FORWARD (buffer->props.direction))
diff --git a/src/hb-ot-layout.hh b/src/hb-ot-layout.hh
index 52dafbba4..938b9a696 100644
--- a/src/hb-ot-layout.hh
+++ b/src/hb-ot-layout.hh
@@ -387,7 +387,7 @@ static inline void
 _hb_ot_layout_reverse_graphemes (hb_buffer_t *buffer)
 {
   buffer->reverse_groups (_hb_grapheme_group_func,
-			  buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS);
+			  HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE (buffer->cluster_level));
 }
 
 static inline bool
diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 6eecc1a10..0469d5981 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -551,7 +551,7 @@ hb_form_clusters (hb_buffer_t *buffer)
   if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII))
     return;
 
-  if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
+  if (HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES (buffer->cluster_level))
     foreach_grapheme (buffer, start, end)
       buffer->merge_clusters (start, end);
   else
@@ -609,7 +609,7 @@ hb_ensure_native_direction (hb_buffer_t *buffer)
    * Ogham fonts are supposed to be implemented BTT or not.  Need to research that
    * first. */
   if ((HB_DIRECTION_IS_HORIZONTAL (direction) &&
-       direction != horiz_dir && horiz_dir != HB_DIRECTION_INVALID) ||
+       direction != horiz_dir && HB_DIRECTION_IS_VALID (horiz_dir)) ||
       (HB_DIRECTION_IS_VERTICAL   (direction) &&
        direction != HB_DIRECTION_TTB))
   {
diff --git a/src/hb-ot-shaper-hangul.cc b/src/hb-ot-shaper-hangul.cc
index c90476bc4..50ea53272 100644
--- a/src/hb-ot-shaper-hangul.cc
+++ b/src/hb-ot-shaper-hangul.cc
@@ -298,8 +298,7 @@ preprocess_text_hangul (const hb_ot_shape_plan_t *plan HB_UNUSED,
 	  end = start + 2;
 	if (unlikely (!buffer->successful))
 	  break;
-	if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
-	  buffer->merge_out_clusters (start, end);
+	buffer->merge_out_clusters (start, end);
 	continue;
       }
     }
@@ -372,8 +371,7 @@ preprocess_text_hangul (const hb_ot_shape_plan_t *plan HB_UNUSED,
 	  if (i < end)
 	    info[i++].hangul_shaping_feature() = TJMO;
 
-	  if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
-	    buffer->merge_out_clusters (start, end);
+	  buffer->merge_out_clusters (start, end);
 	  continue;
 	}
 	else if ((!tindex && buffer->idx + 1 < count && isT (buffer->cur(+1).codepoint)))
diff --git a/src/hb-ot-shaper-thai.cc b/src/hb-ot-shaper-thai.cc
index 6cd67cde3..6124a2114 100644
--- a/src/hb-ot-shaper-thai.cc
+++ b/src/hb-ot-shaper-thai.cc
@@ -360,7 +360,7 @@ preprocess_text_thai (const hb_ot_shape_plan_t *plan,
     {
       /* Since we decomposed, and NIKHAHIT is combining, merge clusters with the
        * previous cluster. */
-      if (start && buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
+      if (start)
 	buffer->merge_out_clusters (start - 1, end);
     }
   }