diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
new file mode 100644
index 37c38c1..720f130
*** a/contrib/pg_upgrade/check.c
--- b/contrib/pg_upgrade/check.c
*************** check_old_cluster(migratorContext *ctx, 
*** 72,77 ****
--- 72,78 ----
  	{
  		old_8_3_check_for_name_data_type_usage(ctx, CLUSTER_OLD);
  		old_8_3_check_for_tsquery_usage(ctx, CLUSTER_OLD);
+ 		old_8_3_check_ltree_usage(ctx, CLUSTER_OLD);
  		if (ctx->check)
  		{
  			old_8_3_rebuild_tsvector_tables(ctx, true, CLUSTER_OLD);
diff --git a/contrib/pg_upgrade/pg_upgrade.h b/contrib/pg_upgrade/pg_upgrade.h
new file mode 100644
index 41c4b11..7a02fa1
*** a/contrib/pg_upgrade/pg_upgrade.h
--- b/contrib/pg_upgrade/pg_upgrade.h
*************** void old_8_3_check_for_name_data_type_us
*** 394,399 ****
--- 394,401 ----
  									   Cluster whichCluster);
  void old_8_3_check_for_tsquery_usage(migratorContext *ctx,
  								Cluster whichCluster);
+ void old_8_3_check_ltree_usage(migratorContext *ctx,
+ 								Cluster whichCluster);
  void old_8_3_rebuild_tsvector_tables(migratorContext *ctx,
  								bool check_mode, Cluster whichCluster);
  void old_8_3_invalidate_hash_gin_indexes(migratorContext *ctx,
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 6fcd61b..7e3a7aa
*** 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(migrator
*** 204,209 ****
--- 204,289 ----
  
  
  /*
+  *	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(migratorContext *ctx, Cluster whichCluster)
+ {
+ 	ClusterInfo *active_cluster = (whichCluster == CLUSTER_OLD) ?
+ 	&ctx->old : &ctx->new;
+ 	int			dbnum;
+ 	FILE	   *script = NULL;
+ 	bool		found = false;
+ 	char		output_path[MAXPGPATH];
+ 
+ 	prep_status(ctx, "Checking for /contrib/ltree");
+ 
+ 	snprintf(output_path, sizeof(output_path), "%s/contrib_ltree.txt",
+ 			 ctx->cwd);
+ 
+ 	for (dbnum = 0; dbnum < active_cluster->dbarr.ndbs; dbnum++)
+ 	{
+ 		PGresult   *res;
+ 		bool		db_used = false;
+ 		int			ntups;
+ 		int			rowno;
+ 		int			i_nspname,
+ 					i_proname;
+ 		DbInfo	   *active_db = &active_cluster->dbarr.dbs[dbnum];
+ 		PGconn	   *conn = connectToServer(ctx, active_db->db_name, whichCluster);
+ 
+ 		/* Find any functions coming from contrib/ltree */
+ 		res = executeQueryOrDie(ctx, 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(ctx, PG_FATAL, "Could not create necessary file:  %s\n", output_path);
+ 			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 (found)
+ 	{
+ 		fclose(script);
+ 		pg_log(ctx, PG_REPORT, "fatal\n");
+ 		pg_log(ctx, 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"
+ 			   "| \t%s\n\n", output_path);
+ 	}
+ 	else
+ 		check_ok(ctx);
+ }
+ 
+ 
+ /*
   * 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 31f1c3d..74fba2e
*** a/doc/src/sgml/pgupgrade.sgml
--- b/doc/src/sgml/pgupgrade.sgml
*************** psql --username postgres --file script.s
*** 465,470 ****
--- 465,475 ----
    </para>
  
    <para>
+    pg_upgrade will not work if the <filename>ltree</>
+    contrib module is installed in a database.
+   </para>
+ 
+   <para>
     You must drop any such columns and migrate them manually.
    </para>