Error on no records to update?

OK.. really never considered this before, so I'm asking as Google results haven't paid off for me on this one.. 

I have a VERY SPECIFIC,  UPDATE query in my .NET program.  without getting into too much detail, I want to update a record where 4 fields match in two different tables.  So far the code is working quite well, but there have been one or two cases (out of 1000 or so records) where a matching record to update was not found.  Which, to SQL, it doesn't care if it doesn't find a matching record to update..  BUT I CARE because this is labor reporting and timekeeping.

Is there any way in my query to get an error if a matching record is NOT found? 

I can come up with a workaround if needed.. but would prefer to have it in my query if possible.

Thanks!