standard errors of marginal effects in multinomial logit

Deat R users,

I am looking for a way to get standard errors of marginal effects of multinomial logit model.

So far I have estimated coeficients of multinomial logit and covariance matrix of coefficients. 
I also managed to obtain marginal effects. However, I can not find a way to find standard errors (which
in theory has to be done using delta method). 

Thanks a lot in advance,
Kremena