  We construct a $Q$-matrix for the eight-vertex model at roots of unity for
crossing parameter $\eta=2mK/L$ with odd $L$, a case for which the existing
constructions do not work. The new $Q$-matrix $\Q$ depends as usual on the
spectral parameter and also on a free parameter $t$. For $t=0$ $\Q$ has the
standard properties. For $t\neq 0$, however, it does not commute with the
operator $S$ and not with itself for different values of the spectral
parameter. We show that the six-vertex limit of $\Q(v,t=iK'/2)$ exists.
