UNION ALL returns "conversion... overflowed an int column"

I had a stored procedure throwing the following error:

The conversion of the varchar value '9999999999' overflowed an int column.  

There's two queries joined, so I split them up to see which one was throwing the error.  

Neither.  Of course.  : - \

If you break the query apart, both halves work.  

Okay, so let's figure this out:

exec sp_describe_first_result_set @tsql = N'myqueryhere'

exec sp_describe_first_result_set @tsql = N'myotherqueryhere'

Oh, hey look, varchar in one, int in the other.

Cause? My own stupidness from 7 years ago:

case when fielda is null or fielda = 0 then 0

else replace(replace(convert(varchar(14),fielda(,'.',''))

end

On one set of data, there are fields that have values, specifically the 9999999999; the second set returns nothing.  

So it tries to convert to the "least" datatype, the INT, and the 9,999,999,999 is too large for INT, so it fails.