diff --git a/src/hb-buffer-private.hh b/src/hb-buffer-private.hh
index 111078c..4983f84 100644
--- a/src/hb-buffer-private.hh
+++ b/src/hb-buffer-private.hh
@@ -124,6 +124,11 @@
   hb_codepoint_t context[2][CONTEXT_LENGTH];
   unsigned int context_len[2];
 
+  /* Debugging */
+  hb_buffer_message_func_t message_func;
+  void *message_data;
+  hb_destroy_func_t message_destroy;
+
 
   /* Methods */
 
@@ -233,6 +238,19 @@
   inline void clear_context (unsigned int side) { context_len[side] = 0; }
 
   HB_INTERNAL void sort (unsigned int start, unsigned int end, int(*compar)(const hb_glyph_info_t *, const hb_glyph_info_t *));
+
+  inline bool messaging (void) { return unlikely (message_func); }
+  inline bool message (hb_font_t *font, const char *fmt, ...) HB_PRINTF_FUNC(3, 4)
+  {
+    if (!messaging ())
+      return true;
+    va_list ap;
+    va_start (ap, fmt);
+    bool ret = message_impl (font, fmt, ap);
+    va_end (ap);
+    return ret;
+  }
+  HB_INTERNAL bool message_impl (hb_font_t *font, const char *fmt, va_list ap) HB_PRINTF_FUNC(3, 0);
 };
 
 
diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index c271086..764b8ed 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -798,6 +798,8 @@
 
   free (buffer->info);
   free (buffer->pos);
+  if (buffer->message_destroy)
+    buffer->message_destroy (buffer->message_data);
 
   free (buffer);
 }
@@ -1713,3 +1715,45 @@
     }
   }
 }
+
+/*
+ * Debugging.
+ */
+
+/**
+ * hb_buffer_set_message_func:
+ * @buffer: a buffer.
+ * @func: (closure user_data) (destroy destroy) (scope notified):
+ * @user_data:
+ * @destroy:
+ *
+ * 
+ *
+ * Since: 1.1.3
+ **/
+void
+hb_buffer_set_message_func (hb_buffer_t *buffer,
+			    hb_buffer_message_func_t func,
+			    void *user_data, hb_destroy_func_t destroy)
+{
+  if (buffer->message_destroy)
+    buffer->message_destroy (buffer->message_data);
+
+  if (func) {
+    buffer->message_func = func;
+    buffer->message_data = user_data;
+    buffer->message_destroy = destroy;
+  } else {
+    buffer->message_func = NULL;
+    buffer->message_data = NULL;
+    buffer->message_destroy = NULL;
+  }
+}
+
+bool
+hb_buffer_t::message_impl (hb_font_t *font, const char *fmt, va_list ap)
+{
+  char buf[100];
+  vsnprintf (buf, sizeof (buf),  fmt, ap);
+  return (bool) this->message_func (this, font, buf, this->message_data);
+}
diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index d3a2512..a28d47f 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -373,6 +373,21 @@
 			      hb_buffer_serialize_format_t format);
 
 
+/*
+ * Debugging.
+ */
+
+typedef hb_bool_t	(*hb_buffer_message_func_t)	(hb_buffer_t *buffer,
+							 hb_font_t   *font,
+							 const char  *message,
+							 void        *user_data);
+
+HB_EXTERN void
+hb_buffer_set_message_func (hb_buffer_t *buffer,
+			    hb_buffer_message_func_t func,
+			    void *user_data, hb_destroy_func_t destroy);
+
+
 HB_END_DECLS
 
 #endif /* HB_BUFFER_H */
diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 6bb4059..3049fa1 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1014,23 +1014,15 @@
     const stage_map_t *stage = &stages[table_index][stage_index];
     for (; i < stage->last_lookup; i++)
     {
-#if 0
-      char buf[4096];
-      hb_buffer_serialize_glyphs (buffer, 0, buffer->len,
-				  buf, sizeof (buf), NULL,
-				  font,
-				  HB_BUFFER_SERIALIZE_FORMAT_TEXT,
-				  HB_BUFFER_SERIALIZE_FLAG_DEFAULT);
-      printf ("buf: [%s]\n", buf);
-#endif
-
       unsigned int lookup_index = lookups[table_index][i].index;
+      if (!buffer->message (font, "start lookup %d", lookup_index)) continue;
       c.set_lookup_index (lookup_index);
       c.set_lookup_mask (lookups[table_index][i].mask);
       c.set_auto_zwj (lookups[table_index][i].auto_zwj);
       apply_string<Proxy> (&c,
 			   proxy.table.get_lookup (lookup_index),
 			   proxy.accels[lookup_index]);
+      (void) buffer->message (font, "end lookup %d", lookup_index);
     }
 
     if (stage->pause_func)