diff --git a/tests/zfs-tests/tests/functional/alloc_class/alloc_class_009_pos.ksh b/tests/zfs-tests/tests/functional/alloc_class/alloc_class_009_pos.ksh
index 7c1d6e15c..e8061fdab 100755
--- a/tests/zfs-tests/tests/functional/alloc_class/alloc_class_009_pos.ksh
+++ b/tests/zfs-tests/tests/functional/alloc_class/alloc_class_009_pos.ksh
@@ -13,7 +13,7 @@
 
 #
 # Copyright (c) 2017, Intel Corporation.
-# Copyright (c) 2018 by Delphix. All rights reserved.
+# Copyright (c) 2018, 2020 by Delphix. All rights reserved.
 #
 
 . $STF_SUITE/tests/functional/alloc_class/alloc_class.kshlib
@@ -33,22 +33,33 @@ log_must disk_setup
 
 typeset stype=""
 typeset sdisks=""
+typeset props=""
 
 for type in "" "mirror" "raidz"
 do
 	if [ "$type" = "mirror" ]; then
 		stype="mirror"
 		sdisks="${CLASS_DISK0} ${CLASS_DISK1} ${CLASS_DISK2}"
+		props="-o ashift=12"
 	elif [ "$type" = "raidz" ]; then
 		stype="mirror"
 		sdisks="${CLASS_DISK0} ${CLASS_DISK1}"
 	else
 		stype=""
-		special_args="${CLASS_DISK0}"
+		sdisks="${CLASS_DISK0}"
+	fi
+
+	#
+	# 1/3 of the time add the special vdev after creating the pool
+	#
+	if [ $((RANDOM % 3)) -eq 0 ]; then
+		log_must zpool create ${props} $TESTPOOL $type $ZPOOL_DISKS
+		log_must zpool add ${props} $TESTPOOL special $stype $sdisks
+	else
+		log_must zpool create ${props} $TESTPOOL $type $ZPOOL_DISKS \
+		    special $stype $sdisks
 	fi
 
-	log_must zpool create $TESTPOOL $type $ZPOOL_DISKS \
-	    special $stype $sdisks
 	log_must zpool export $TESTPOOL
 	log_must zpool import -d $TEST_BASE_DIR -s $TESTPOOL
 	log_must display_status $TESTPOOL