Sum of Null Values

[depawl]

I have a query set up to sum 2 fields to a 3rd field, for example, I have
field1, field2, and field3.
Fields 1 and 2 are data from a table.
In Field3 I have an expression:
Field3: [Field1] + [Field2]
This works fine except when either Field1 and/or Field2 contain no data, then the sum does not work. Any ideas how to correct this?
I realize this may not be the best way to accomplish what I am trying to do but this is a small part of a very large application and i would like to change as little as possible since everything else is working ok.
Thanks very much.

 

[pbaldy]

Field3: Nz([Field1],0) + Nz([Field2],0)

 

[depawl]

Thanks pbaldy. That did the trick.