diff --git a/src/hb-ot-shape-complex-khmer.cc b/src/hb-ot-shape-complex-khmer.cc
index 18e3c941e..7876d3666 100644
--- a/src/hb-ot-shape-complex-khmer.cc
+++ b/src/hb-ot-shape-complex-khmer.cc
@@ -372,22 +372,25 @@ initial_reordering_consonant_syllable (const hb_ot_shape_plan_t *plan,
 	break;
       }
 
-    /* Note!  syllable() is a one-byte field. */
-    for (unsigned int i = base; i < end; i++)
-      if (info[i].syllable() != 255)
-      {
-	unsigned int max = i;
-	unsigned int j = start + info[i].syllable();
-	while (j != i)
+    if (unlikely (end - start >= 127))
+      buffer->merge_clusters (start, end);
+    else
+      /* Note!  syllable() is a one-byte field. */
+      for (unsigned int i = base; i < end; i++)
+	if (info[i].syllable() != 255)
 	{
-	  max = MAX (max, j);
-	  unsigned int next = start + info[j].syllable();
-	  info[j].syllable() = 255; /* So we don't process j later again. */
-	  j = next;
+	  unsigned int max = i;
+	  unsigned int j = start + info[i].syllable();
+	  while (j != i)
+	  {
+	    max = MAX (max, j);
+	    unsigned int next = start + info[j].syllable();
+	    info[j].syllable() = 255; /* So we don't process j later again. */
+	    j = next;
+	  }
+	  if (i != max)
+	    buffer->merge_clusters (i, max + 1);
 	}
-	if (i != max)
-	  buffer->merge_clusters (i, max + 1);
-      }
 
     /* Put syllable back in. */
     for (unsigned int i = start; i < end; i++)