diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 085ae68731..1c4812cd86 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -1852,13 +1852,10 @@ vdev_open(vdev_t *vd)
 
 	/*
 	 * Track the min and max ashift values for normal data devices.
-	 *
-	 * DJB - TBD these should perhaps be tracked per allocation class
-	 * (e.g. spa_min_ashift is used to round up post compression buffers)
 	 */
 	if (vd->vdev_top == vd && vd->vdev_ashift != 0 &&
 	    vd->vdev_alloc_bias == VDEV_BIAS_NONE &&
-	    vd->vdev_aux == NULL) {
+	    vd->vdev_islog == 0 && vd->vdev_aux == NULL) {
 		if (vd->vdev_ashift > spa->spa_max_ashift)
 			spa->spa_max_ashift = vd->vdev_ashift;
 		if (vd->vdev_ashift < spa->spa_min_ashift)