  We prove that, over any field, the dimension of the indeterminacy locus of a
rational transformation $f$ of $P^n$ which is defined by monomials of the same
degree $d$ with no common factors is at least $(n-2)/2$, provided that the
degree of $f$ as a map is not divisible by $d$. This implies upper bounds on
the multidegree of $f$.
