I'm trying to fix an issue with a legacy database. The quote_literal function is not working for a specific database on an 8.4 install of postgres.

Here's my results on a fresh test database:

select quote_literal(42);
 quote_literal 
---------------
 '42'
(1 row)

And now the same on the target db

select quote_literal(42);
ERROR:  function quote_literal(integer) is not unique
LINE 1: select quote_literal(42);
           ^
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.

AIUI, the quote_literal(anyvalue) function should handle integer values ok, and this seems to be upheld by the first test.

So I figured the quote_literal function must have been overridden in this db but no this doesn't seem to be the case. I could override it with a specific quote_literal(integer) function but I don't see why I should have to.

The question is what is could be causing the failure of this function in this specific database whilst not affecting the fresh db?