  We consider the standard model of i.i.d. first passage percolation on
$\mathbb{Z}^d$ given a distribution $G$ on $[0,+\infty]$ ($+\infty$ is
allowed). When $G([0,+\infty]) < p_c(d)$, it is known that the time constant
$\mu_G$ exists. We are interested in the regularity properties of the map
$G\mapsto\mu_G$. We first study the specific case of distributions of the form
$G_p=p\delta_1+(1-p)\delta_\infty$ for $p>p_c(d)$. In this case, the travel
time between two points is equal to the length of the shortest path between the
two points in a bond percolation of parameter $p$. We show that the function
$p\mapsto \mu_{G_p}$ is Lipschitz continuous on every interval $[p_0,1]$, where
$p_0>p_c(d)$.
