Ghost parameter in Update Query

[Bob Phillips]

I am sure I am missing the obvious, but here goes anyway.

I have written hundreds of parameterised queries in Access, but I don't recall having this problem before. The following update that should prompt for 3 values prompts for4, an extra value.

UPDATE Product 
SET ProductName = param.product, ProductType = param.product.type
WHERE Id = param.id;

As well as the 3 parameters that I have setup, it also prompts for ProductType. What am I missing here?