typedef struct _notmuch_doc_id_set notmuch_doc_id_set_t;
 
+typedef struct _notmuch_string_list notmuch_string_list_t;
+
 /* database.cc */
 
 /* Lookup a prefix value by name.
                        notmuch_database_t *notmuch,
                        unsigned int seed_doc_id,
                        notmuch_doc_id_set_t *match_set,
+                       notmuch_string_list_t *excluded_terms,
                        notmuch_sort_t sort);
 
 /* message.cc */
     struct _notmuch_string_node *next;
 } notmuch_string_node_t;
 
-typedef struct visible _notmuch_string_list {
+struct visible _notmuch_string_list {
     int length;
     notmuch_string_node_t *head;
     notmuch_string_node_t **tail;
-} notmuch_string_list_t;
+};
 
 notmuch_string_list_t *
 _notmuch_string_list_create (const void *ctx);
 
 /* Get the number of messages in 'thread' that matched the search.
  *
  * This count includes only the messages in this thread that were
- * matched by the search from which the thread was created. Contrast
- * with notmuch_thread_get_total_messages() .
+ * matched by the search from which the thread was created and were
+ * not excluded by any exclude tags passed in with the query (see
+ * notmuch_query_add_tag_exclude). Contrast with
+ * notmuch_thread_get_total_messages() .
  */
 int
 notmuch_thread_get_matched_messages (notmuch_thread_t *thread);
 
  */
 static void
 _thread_add_message (notmuch_thread_t *thread,
-                    notmuch_message_t *message)
+                    notmuch_message_t *message,
+                    notmuch_string_list_t *exclude_terms)
 {
     notmuch_tags_t *tags;
     const char *tag;
         notmuch_tags_move_to_next (tags))
     {
        tag = notmuch_tags_get (tags);
+       /* Mark excluded messages. */
+       for (notmuch_string_node_t *term = exclude_terms->head; term;
+            term = term->next) {
+           /* We ignore initial 'K'. */
+           if (strcmp(tag, (term->string + 1)) == 0) {
+               notmuch_message_set_flag (message, NOTMUCH_MESSAGE_FLAG_EXCLUDED, TRUE);
+               break;
+           }
+       }
        g_hash_table_insert (thread->tags, xstrdup (tag), NULL);
     }
 }
            _thread_set_subject_from_message (thread, message);
     }
 
-    thread->matched_messages++;
+    if (!notmuch_message_get_flag (message, NOTMUCH_MESSAGE_FLAG_EXCLUDED))
+       thread->matched_messages++;
 
     if (g_hash_table_lookup_extended (thread->message_hash,
                            notmuch_message_get_message_id (message), NULL,
                        notmuch_database_t *notmuch,
                        unsigned int seed_doc_id,
                        notmuch_doc_id_set_t *match_set,
+                       notmuch_string_list_t *exclude_terms,
                        notmuch_sort_t sort)
 {
     notmuch_thread_t *thread;
        if (doc_id == seed_doc_id)
            message = seed_message;
 
-       _thread_add_message (thread, message);
+       _thread_add_message (thread, message, exclude_terms);
 
        if ( _notmuch_doc_id_set_contains (match_set, doc_id)) {
            _notmuch_doc_id_set_remove (match_set, doc_id);