Force Value In Userform Textbox

I have a UserForm that requires a value in TextBox10. I load a "1" into it at start up. If the user tries to delete the value in TextBox10 and exit, leaving either "" or 0 in the TextBox, it will cause a great many problems. I need someway to keep the focus in TextBox10.

I tried to find something using the search engine but I could not find anything searching with this subject.

Here is the code from my first attempt:

Private Sub TextBox10_Exit(ByVal Cancel As MSForms.ReturnBoolean)

If TextBox10.Value = 0 Or TextBox10.Value = vbNullString Then
TextBox10.SetFocus
Exit Sub
End If

It doesn't seem to do anything. When I delete whatever is in the Textbox and hit enter, it should just stay in TextBox10 but instead it goes to the next tab location.