diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
new file mode 100644
index 79b6c3c..b216e61
*** a/contrib/pg_upgrade/check.c
--- b/contrib/pg_upgrade/check.c
***************
*** 9,14 ****
--- 9,15 ----
  
  #include "postgres_fe.h"
  
+ #include "catalog/pg_authid.h"
  #include "mb/pg_wchar.h"
  #include "pg_upgrade.h"
  
*************** static void check_locale_and_encoding(Co
*** 19,25 ****
  						  ControlData *newctrl);
  static bool equivalent_locale(const char *loca, const char *locb);
  static bool equivalent_encoding(const char *chara, const char *charb);
! static void check_is_super_user(ClusterInfo *cluster);
  static void check_for_prepared_transactions(ClusterInfo *cluster);
  static void check_for_isn_and_int8_passing_mismatch(ClusterInfo *cluster);
  static void check_for_reg_data_type_usage(ClusterInfo *cluster);
--- 20,26 ----
  						  ControlData *newctrl);
  static bool equivalent_locale(const char *loca, const char *locb);
  static bool equivalent_encoding(const char *chara, const char *charb);
! static void check_is_install_user(ClusterInfo *cluster);
  static void check_for_prepared_transactions(ClusterInfo *cluster);
  static void check_for_isn_and_int8_passing_mismatch(ClusterInfo *cluster);
  static void check_for_reg_data_type_usage(ClusterInfo *cluster);
*************** check_and_dump_old_cluster(bool live_che
*** 94,100 ****
  	/*
  	 * Check for various failure cases
  	 */
! 	check_is_super_user(&old_cluster);
  	check_for_prepared_transactions(&old_cluster);
  	check_for_reg_data_type_usage(&old_cluster);
  	check_for_isn_and_int8_passing_mismatch(&old_cluster);
--- 95,101 ----
  	/*
  	 * Check for various failure cases
  	 */
! 	check_is_install_user(&old_cluster);
  	check_for_prepared_transactions(&old_cluster);
  	check_for_reg_data_type_usage(&old_cluster);
  	check_for_isn_and_int8_passing_mismatch(&old_cluster);
*************** check_new_cluster(void)
*** 158,179 ****
  	if (user_opts.transfer_mode == TRANSFER_MODE_LINK)
  		check_hard_link();
  
! 	check_is_super_user(&new_cluster);
! 
! 	/*
! 	 * We don't restore our own user, so both clusters must match have
! 	 * matching install-user oids.
! 	 */
! 	if (old_cluster.install_role_oid != new_cluster.install_role_oid)
! 		pg_fatal("Old and new cluster install users have different values for pg_authid.oid.\n");
! 
! 	/*
! 	 * We only allow the install user in the new cluster because other defined
! 	 * users might match users defined in the old cluster and generate an
! 	 * error during pg_dump restore.
! 	 */
! 	if (new_cluster.role_count != 1)
! 		pg_fatal("Only the install user can be defined in the new cluster.\n");
  
  	check_for_prepared_transactions(&new_cluster);
  }
--- 159,165 ----
  	if (user_opts.transfer_mode == TRANSFER_MODE_LINK)
  		check_hard_link();
  
! 	check_is_install_user(&new_cluster);
  
  	check_for_prepared_transactions(&new_cluster);
  }
*************** create_script_for_old_cluster_deletion(c
*** 698,714 ****
  
  
  /*
!  *	check_is_super_user()
   *
!  *	Check we are superuser, and output user id and user count
   */
  static void
! check_is_super_user(ClusterInfo *cluster)
  {
  	PGresult   *res;
  	PGconn	   *conn = connectToServer(cluster, "template1");
  
! 	prep_status("Checking database user is a superuser");
  
  	/* Can't use pg_authid because only superusers can view it. */
  	res = executeQueryOrDie(conn,
--- 684,701 ----
  
  
  /*
!  *	check_is_install_user()
   *
!  *	Check we are the install user, and that the new cluster
!  *	has no other users.
   */
  static void
! check_is_install_user(ClusterInfo *cluster)
  {
  	PGresult   *res;
  	PGconn	   *conn = connectToServer(cluster, "template1");
  
! 	prep_status("Checking database user is the install user");
  
  	/* Can't use pg_authid because only superusers can view it. */
  	res = executeQueryOrDie(conn,
*************** check_is_super_user(ClusterInfo *cluster
*** 716,727 ****
  							"FROM pg_catalog.pg_roles "
  							"WHERE rolname = current_user");
  
! 	if (PQntuples(res) != 1 || strcmp(PQgetvalue(res, 0, 0), "t") != 0)
! 		pg_fatal("database user \"%s\" is not a superuser\n",
  				 os_info.user);
  
- 	cluster->install_role_oid = atooid(PQgetvalue(res, 0, 1));
- 
  	PQclear(res);
  
  	res = executeQueryOrDie(conn,
--- 703,718 ----
  							"FROM pg_catalog.pg_roles "
  							"WHERE rolname = current_user");
  
! 	/*
! 	 * We only allow the install user in the new cluster (see comment below)
! 	 * and we preserve pg_authid.oid, so this must be the install user in
! 	 * the old cluster too.
! 	 */
! 	if (PQntuples(res) != 1 ||
! 		atooid(PQgetvalue(res, 0, 1)) != BOOTSTRAP_SUPERUSERID)
! 		pg_fatal("database user \"%s\" is not the install user\n",
  				 os_info.user);
  
  	PQclear(res);
  
  	res = executeQueryOrDie(conn,
*************** check_is_super_user(ClusterInfo *cluster
*** 731,737 ****
  	if (PQntuples(res) != 1)
  		pg_fatal("could not determine the number of users\n");
  
! 	cluster->role_count = atoi(PQgetvalue(res, 0, 0));
  
  	PQclear(res);
  
--- 722,734 ----
  	if (PQntuples(res) != 1)
  		pg_fatal("could not determine the number of users\n");
  
! 	/*
! 	 * We only allow the install user in the new cluster because other defined
! 	 * users might match users defined in the old cluster and generate an
! 	 * error during pg_dump restore.
! 	 */
! 	if (cluster == &new_cluster && atooid(PQgetvalue(res, 0, 0)) != 1)
! 		pg_fatal("Only the install user can be defined in the new cluster.\n");
  
  	PQclear(res);
  
diff --git a/contrib/pg_upgrade/pg_upgrade.h b/contrib/pg_upgrade/pg_upgrade.h
new file mode 100644
index 0410b02..61e5de0
*** a/contrib/pg_upgrade/pg_upgrade.h
--- b/contrib/pg_upgrade/pg_upgrade.h
*************** typedef struct
*** 256,263 ****
  	char		major_version_str[64];	/* string PG_VERSION of cluster */
  	uint32		bin_version;	/* version returned from pg_ctl */
  	Oid			pg_database_oid;	/* OID of pg_database relation */
- 	Oid			install_role_oid;		/* OID of connected role */
- 	Oid			role_count;		/* number of roles defined in the cluster */
  	const char *tablespace_suffix;		/* directory specification */
  } ClusterInfo;
  
--- 256,261 ----