diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
index 93b9e695b7..ea7464871e 100644
--- a/contrib/pg_upgrade/check.c
+++ b/contrib/pg_upgrade/check.c
@@ -81,6 +81,7 @@ check_old_cluster(bool live_check, char **sequence_script_file_name)
 	{
 		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
index feea324bd5..2abd91771f 100644
--- a/contrib/pg_upgrade/pg_upgrade.h
+++ b/contrib/pg_upgrade/pg_upgrade.h
@@ -411,6 +411,7 @@ void new_9_0_populate_pg_largeobject_metadata(ClusterInfo *cluster,
 
 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
index 55d919cf07..625f4ad63a 100644
--- a/contrib/pg_upgrade/version_old_8_3.c
+++ b/contrib/pg_upgrade/version_old_8_3.c
@@ -201,6 +201,87 @@ old_8_3_check_for_tsquery_usage(ClusterInfo *cluster)
 }
 
 
+/*
+ *	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
diff --git a/doc/src/sgml/pgupgrade.sgml b/doc/src/sgml/pgupgrade.sgml
index 2d8bbce6b4..9b0718df6b 100644
--- a/doc/src/sgml/pgupgrade.sgml
+++ b/doc/src/sgml/pgupgrade.sgml
@@ -487,6 +487,11 @@ psql --username postgres --file script.sql postgres
    You must drop any such columns and upgrade them manually.
   </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>