An astragal boot for mounting onto a lower end of an astragal includes a platform, a first and second lateral fin spaced from each other and projecting downwardly from the platform, and an auxiliary fin disposed between the first and second lateral fins. The auxiliary fin defines an auxiliary fin edge extending from the first lateral fin to the second lateral fin for sealing engagement with the threshold. The auxiliary fin includes a hub portion and a first and second leg portion each extending from the hub portion to the first and second lateral fins, respectively. The first leg portion extends along a first direction defining a portion of the auxiliary fin edge along the first direction and the second leg portion extends along a second direction at an obtuse angle relative to the first direction defining another portion of the auxiliary fin edge along the second direction.