[exim] Help with "if" syntax

Hi

I have an ACL entry that pulls a value from a SQL database. If the
database is unavailable, I'd like the entry to default to a sensible figure.

So far I have this:

warn set acl_m6 = ${if eq{${lookup pgsql{ATTHRESH}}{0}{60}{${lookup
pgsql{ATTHRESH}}}

Which gives the error:

    syntax error in "if" item - "fail" expected

Looking at the documentation for if, I can't make sense of why this is
expecting "fail" nor where I should place it.

Any pointers would be greatly appreciated.

Thanks

Martin A. Brooks