Labeling multi-line equation not working as expected

My aim is to set the label of the following equation to right as usual. The difference is that here I have two lines which messes this labeling up.

documentclass[12pt]{article} 
usepackage{amsmath}

begin{document}
begin{equation}label{weight} 
omega_{x_R} = begin{cases}
   {1 over N, & text{if } N ge 1 
    1, & text{otherwise }
end{equation}

end{document}

See the following:

documentclass[12pt]{article} 
usepackage{amsmath}

begin{document}
begin{equation}label{weight} 
omega_{x_R} = begin{cases}
   frac{1}{N}, & text{if } N ge 1 
    1, & text{otherwise }
    end{cases}
end{equation}

end{document}