Jade Warning ("missing space before text") on seemingly working line of code

Question

So, playing around with Jade, and have the following simple form:

form(method='post')#newCustomer
    fieldset
        legend Personal
        .row
            .small-7.column
                #[label First Name #[span.muted Required] #[input(name='firstName')]]
        .row
            .small-7.column
                #[label Surname #[span.muted Required] #[input(name='surname')]]
        .row
            .small-7.column
                #[label E-Mail Address #[span.muted Required] #[input(type='email' name='email')]]

The HTML it produces is fine, and works as I want. The compiler complains though, giving lines akin to the following:

Warning: missing space before text for line 10 of jade file

The lines it complains about are the ones beginning with the #[label]. It's not a huge deal because, as I say, the HTML is correct, but I'd like to squash the warning if possible.

Thanks in advance.