diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 54c33a3e1..8cd8fcc17 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -275,8 +275,7 @@ hb_insert_dotted_circle (hb_buffer_t *buffer, hb_font_t *font)
 static void
 hb_form_clusters (hb_buffer_t *buffer)
 {
-  if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII) ||
-      buffer->cluster_level != HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
+  if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII))
     return;
 
   /* Loop duplicated in hb_ensure_native_direction(), and in _hb-coretext.cc */
@@ -288,11 +287,17 @@ hb_form_clusters (hb_buffer_t *buffer)
     if (likely (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&info[i])) &&
 		!_hb_glyph_info_is_joiner (&info[i])))
     {
-      buffer->merge_clusters (base, i);
+      if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
+	buffer->merge_clusters (base, i);
+      else
+	buffer->unsafe_to_break (base, i);
       base = i;
     }
   }
-  buffer->merge_clusters (base, count);
+  if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
+    buffer->merge_clusters (base, count);
+  else
+    buffer->unsafe_to_break (base, count);
 }
 
 static void
@@ -580,8 +585,6 @@ hb_ot_substitute_default (hb_ot_shape_context_t *c)
 {
   hb_buffer_t *buffer = c->buffer;
 
-  hb_ot_shape_initialize_masks (c);
-
   hb_ot_mirror_chars (c);
 
   HB_BUFFER_ALLOCATE_VAR (buffer, glyph_index);
@@ -836,8 +839,10 @@ hb_ot_shape_internal (hb_ot_shape_context_t *c)
 
   c->buffer->clear_output ();
 
+  hb_ot_shape_initialize_masks (c);
   hb_set_unicode_props (c->buffer);
   hb_insert_dotted_circle (c->buffer, c->font);
+
   hb_form_clusters (c->buffer);
 
   hb_ensure_native_direction (c->buffer);