Need help with a conditional formatting expression

[templeowls]

I'm using this below expression to highlight a field if its blank and it works well:

IsNull([CustomerLastName])=True

The only change I want to make is that if a certain other field is blank too (let's say CustomerFirstName) then the CustomerLastName field does not highlight.

Any ideas?

[June7]

So this CF is on CustomerLastName control?

IsNull([CustomerLastName]) AND Not IsNull([CustomerFirstName])

Don't really need =True.

[templeowls]

That worked. Thank you!!