wiki Disk Usage, table size: ERROR: could not open relation with OID 0

Hi

I got the message
ERROR: could not open relation with OID 0
when running the "General Table Size Information" from
https://wiki.postgresql.org/wiki/Disk_Usage

This patch gives some system tables
@@ -12,5 +12,6 @@
FROM pg_class c
LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE relkind = 'r'
+ AND reltoastrelid!=0
) a
) a;

But I guess it was supposed to give size of all tables.

I'm running version 9.1.9 so it should be working according to the wiki.

The original statement:

SELECT *, pg_size_pretty(total_bytes) AS total
, pg_size_pretty(index_bytes) AS INDEX
, pg_size_pretty(toast_bytes) AS toast
, pg_size_pretty(table_bytes) AS TABLE
FROM (
SELECT *, total_bytes-index_bytes-COALESCE(toast_bytes,0) AS
table_bytes FROM (
SELECT c.oid,nspname AS table_schema, relname AS TABLE_NAME
, c.reltuples AS row_estimate
, pg_total_relation_size(c.oid) AS total_bytes
, pg_indexes_size(c.oid) AS index_bytes
, pg_total_relation_size(reltoastrelid) AS toast_bytes
FROM pg_class c
LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE relkind = 'r'
) a) a;

Any help much appreciated.

./best regards