diff --git a/src/bin/pg_upgrade/check.c b/src/bin/pg_upgrade/check.c
new file mode 100644
index 8c034bc..e92fc66
*** a/src/bin/pg_upgrade/check.c
--- b/src/bin/pg_upgrade/check.c
*************** output_completion_banner(char *analyze_s
*** 195,203 ****
  			   deletion_script_file_name);
  	else
  		pg_log(PG_REPORT,
! 			   "Could not create a script to delete the old cluster's data\n"
! 		  "files because user-defined tablespaces exist in the old cluster\n"
! 		"directory.  The old cluster's contents must be deleted manually.\n");
  }
  
  
--- 195,204 ----
  			   deletion_script_file_name);
  	else
  		pg_log(PG_REPORT,
! 		  "Could not create a script to delete the old cluster's data files\n"
! 		  "because the new cluster's data directory or user-defined tablespaces\n"
! 		  "exist in the old cluster directory.  The old cluster's contents must\n"
! 		  "be deleted manually.\n");
  }
  
  
*************** create_script_for_old_cluster_deletion(c
*** 496,513 ****
  {
  	FILE	   *script = NULL;
  	int			tblnum;
! 	char		old_cluster_pgdata[MAXPGPATH];
  
  	*deletion_script_file_name = psprintf("%sdelete_old_cluster.%s",
  										  SCRIPT_PREFIX, SCRIPT_EXT);
  
  	/*
  	 * Some users (oddly) create tablespaces inside the cluster data
  	 * directory.  We can't create a proper old cluster delete script in that
  	 * case.
  	 */
- 	strlcpy(old_cluster_pgdata, old_cluster.pgdata, MAXPGPATH);
- 	canonicalize_path(old_cluster_pgdata);
  	for (tblnum = 0; tblnum < os_info.num_old_tablespaces; tblnum++)
  	{
  		char		old_tablespace_dir[MAXPGPATH];
--- 497,531 ----
  {
  	FILE	   *script = NULL;
  	int			tblnum;
! 	char		old_cluster_pgdata[MAXPGPATH], new_cluster_pgdata[MAXPGPATH];
  
  	*deletion_script_file_name = psprintf("%sdelete_old_cluster.%s",
  										  SCRIPT_PREFIX, SCRIPT_EXT);
  
+ 	strlcpy(old_cluster_pgdata, old_cluster.pgdata, MAXPGPATH);
+ 	canonicalize_path(old_cluster_pgdata);
+ 
+ 	strlcpy(new_cluster_pgdata, new_cluster.pgdata, MAXPGPATH);
+ 	canonicalize_path(new_cluster_pgdata);
+ 
+ 	/* Some people put the new data directory inside the old one. */
+ 	if (path_is_prefix_of_path(old_cluster_pgdata, new_cluster_pgdata))
+ 	{
+ 		pg_log(PG_WARNING,
+ 		   "\nWARNING:  new data directory should not be inside the old data directory, e.g. %s\n", old_cluster_pgdata);
+ 
+ 		/* Unlink file in case it is left over from a previous run. */
+ 		unlink(*deletion_script_file_name);
+ 		pg_free(*deletion_script_file_name);
+ 		*deletion_script_file_name = NULL;
+ 		return;
+ 	}
+ 
  	/*
  	 * Some users (oddly) create tablespaces inside the cluster data
  	 * directory.  We can't create a proper old cluster delete script in that
  	 * case.
  	 */
  	for (tblnum = 0; tblnum < os_info.num_old_tablespaces; tblnum++)
  	{
  		char		old_tablespace_dir[MAXPGPATH];