How to extract an integer value from the NewValues property of DetailsViewUpdateEventArgs?

I have a DetailsView control with Edit, Delete and New buttons. After editing the data in the view, and before updating, I need to validate user input, so I have a DetailsView_ItemUpdating method:

    protected void DetailsView1_ItemUpdating(object sender, DetailsViewUpdateEventArgs e)
    {
       
        lblMsg.Text = "e.NewValues[\"GoalsAgainst\"].ToString() "
                    + e.NewValues["GoalsAgainst"].ToString();

        if (((Int32)(e.NewValues["GoalsFor"]) < 0) || ((Int32)(e.NewValues["GoalsAgainst"]) < 0))
        {
            lblMsg.Text = "Cannot have a negative score";
            e.Cancel = true;
        }
    }

I know that, for example, the data in the "GoalsAgainst" field is a finite integer, because the e.NewValues["GoalsAgainst"].ToString() returns "6". When I try the cast  ((Int32)(e.NewValues["GoalsAgainst"]), however, I get an invalid cast exception, with the additional information that "... When casting from a number, the value must be a number less than infinity."

The online help refers to the "Dictionary" interface, which confuses me more than it helps. What am I missing here?