--- a/usr/src/uts/common/fs/zfs/spa.c	Wed Aug 13 17:34:22 2008 -0700
+++ b/usr/src/uts/common/fs/zfs/spa.c	Wed Aug 13 22:27:55 2008 -0700
@@ -2785,7 +2785,6 @@
 	vdev_t *rvd = spa->spa_root_vdev;
 	vdev_t *oldvd, *newvd, *newrootvd, *pvd, *tvd;
 	vdev_ops_t *pvops;
-	int is_log;
 	dmu_tx_t *tx;
 	char *oldvdpath, *newvdpath;
 	int newvd_isspare;
@@ -2821,8 +2820,7 @@
 	/*
 	 * Spares can't replace logs
 	 */
-	is_log = oldvd->vdev_islog;
-	if (is_log && newvd->vdev_isspare)
+	if (oldvd->vdev_top->vdev_islog && newvd->vdev_isspare)
 		return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
 
 	if (!replacing) {