diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
new file mode 100644
index 93b9e69..ea74648
*** a/contrib/pg_upgrade/check.c
--- b/contrib/pg_upgrade/check.c
*************** check_old_cluster(bool live_check, char 
*** 81,86 ****
--- 81,87 ----
  	{
  		old_8_3_check_for_name_data_type_usage(&old_cluster);
  		old_8_3_check_for_tsquery_usage(&old_cluster);
+ 		old_8_3_check_ltree_usage(&old_cluster);
  		if (user_opts.check)
  		{
  			old_8_3_rebuild_tsvector_tables(&old_cluster, true);
diff --git a/contrib/pg_upgrade/pg_upgrade.h b/contrib/pg_upgrade/pg_upgrade.h
new file mode 100644
index feea324..2abd917
*** a/contrib/pg_upgrade/pg_upgrade.h
--- b/contrib/pg_upgrade/pg_upgrade.h
*************** void new_9_0_populate_pg_largeobject_met
*** 411,416 ****
--- 411,417 ----
  
  void		old_8_3_check_for_name_data_type_usage(ClusterInfo *cluster);
  void		old_8_3_check_for_tsquery_usage(ClusterInfo *cluster);
+ void		old_8_3_check_ltree_usage(ClusterInfo *cluster);
  void		old_8_3_rebuild_tsvector_tables(ClusterInfo *cluster, bool check_mode);
  void		old_8_3_invalidate_hash_gin_indexes(ClusterInfo *cluster, bool check_mode);
  void old_8_3_invalidate_bpchar_pattern_ops_indexes(ClusterInfo *cluster,
diff --git a/contrib/pg_upgrade/version_old_8_3.c b/contrib/pg_upgrade/version_old_8_3.c
new file mode 100644
index 55d919c..625f4ad
*** a/contrib/pg_upgrade/version_old_8_3.c
--- b/contrib/pg_upgrade/version_old_8_3.c
*************** old_8_3_check_for_tsquery_usage(ClusterI
*** 202,207 ****
--- 202,288 ----
  
  
  /*
+  *	old_8_3_check_ltree_usage()
+  *	8.3 -> 8.4
+  *	The internal ltree structure was changed in 8.4 so upgrading is impossible.
+  */
+ void
+ old_8_3_check_ltree_usage(ClusterInfo *cluster)
+ {
+ 	int			dbnum;
+ 	FILE	   *script = NULL;
+ 	bool		found = false;
+ 	char		output_path[MAXPGPATH];
+ 
+ 	prep_status("Checking for contrib/ltree");
+ 
+ 	snprintf(output_path, sizeof(output_path), "%s/contrib_ltree.txt",
+ 			 os_info.cwd);
+ 
+ 	for (dbnum = 0; dbnum < cluster->dbarr.ndbs; dbnum++)
+ 	{
+ 		PGresult   *res;
+ 		bool		db_used = false;
+ 		int			ntups;
+ 		int			rowno;
+ 		int			i_nspname,
+ 					i_proname;
+ 		DbInfo	   *active_db = &cluster->dbarr.dbs[dbnum];
+ 		PGconn	   *conn = connectToServer(cluster, active_db->db_name);
+ 
+ 		/* Find any functions coming from contrib/ltree */
+ 		res = executeQueryOrDie(conn,
+ 								"SELECT n.nspname, p.proname "
+ 								"FROM	pg_catalog.pg_proc p, "
+ 								"		pg_catalog.pg_namespace n "
+ 								"WHERE	p.pronamespace = n.oid AND "
+ 								"		p.probin = '$libdir/ltree'");
+ 
+ 		ntups = PQntuples(res);
+ 		i_nspname = PQfnumber(res, "nspname");
+ 		i_proname = PQfnumber(res, "proname");
+ 		for (rowno = 0; rowno < ntups; rowno++)
+ 		{
+ 			found = true;
+ 			if (script == NULL && (script = fopen(output_path, "w")) == NULL)
+ 				pg_log(PG_FATAL, "Could not open file \"%s\": %s\n",
+ 					   output_path, getErrorText(errno));
+ 			if (!db_used)
+ 			{
+ 				fprintf(script, "Database: %s\n", active_db->db_name);
+ 				db_used = true;
+ 			}
+ 			fprintf(script, "  %s.%s\n",
+ 					PQgetvalue(res, rowno, i_nspname),
+ 					PQgetvalue(res, rowno, i_proname));
+ 		}
+ 
+ 		PQclear(res);
+ 
+ 		PQfinish(conn);
+ 	}
+ 
+ 	if (script)
+ 		fclose(script);
+ 
+ 	if (found)
+ 	{
+ 		pg_log(PG_REPORT, "fatal\n");
+ 		pg_log(PG_FATAL,
+ 			   "Your installation contains the \"ltree\" data type.  This data type\n"
+ 			   "changed its internal storage format between your old and new clusters so this\n"
+ 			   "cluster cannot currently be upgraded.  You can manually upgrade databases\n"
+ 			   "that use \"contrib/ltree\" facilities and remove \"contrib/ltree\" from the old\n"
+ 			   "cluster and restart the upgrade.  A list of the problem functions is in the\n"
+ 			   "file:\n"
+ 			   "    %s\n\n", output_path);
+ 	}
+ 	else
+ 		check_ok();
+ }
+ 
+ 
+ /*
   * old_8_3_rebuild_tsvector_tables()
   *	8.3 -> 8.4
   * 8.3 sorts lexemes by its length and if lengths are the same then it uses
diff --git a/doc/src/sgml/pgupgrade.sgml b/doc/src/sgml/pgupgrade.sgml
new file mode 100644
index 2d8bbce..9b0718d
*** a/doc/src/sgml/pgupgrade.sgml
--- b/doc/src/sgml/pgupgrade.sgml
*************** psql --username postgres --file script.s
*** 488,493 ****
--- 488,498 ----
    </para>
  
    <para>
+    pg_upgrade will not work if the <filename>ltree</>
+    contrib module is installed in a database.
+   </para>
+ 
+   <para>
     pg_upgrade will require a table rebuild if:
     <itemizedlist>
      <listitem>