diff --git a/test/vhost/fiotest/fio.sh b/test/vhost/fiotest/fio.sh
index a395ae0c5..bdd992473 100755
--- a/test/vhost/fiotest/fio.sh
+++ b/test/vhost/fiotest/fio.sh
@@ -119,7 +119,7 @@ rpc_py="$rootdir/scripts/rpc.py -s $(get_vhost_dir 0)/rpc.sock"
 
 for vm_conf in "${vms[@]}"; do
 	IFS=',' read -ra conf <<< "$vm_conf"
-	if [[ x"${conf[0]}" == x"" ]] || ! assert_number ${conf[0]}; then
+	if [[ -z ${conf[0]} ]] || ! assert_number ${conf[0]}; then
 		fail "invalid VM configuration syntax $vm_conf"
 	fi
 
diff --git a/test/vhost/hotplug/common.sh b/test/vhost/hotplug/common.sh
index f89b601b4..edf22fae4 100644
--- a/test/vhost/hotplug/common.sh
+++ b/test/vhost/hotplug/common.sh
@@ -88,7 +88,7 @@ function print_test_fio_header() {
 function vms_setup() {
 	for vm_conf in "${vms[@]}"; do
 		IFS=',' read -ra conf <<< "$vm_conf"
-		if [[ x"${conf[0]}" == x"" ]] || ! assert_number ${conf[0]}; then
+		if [[ -z ${conf[0]} ]] || ! assert_number ${conf[0]}; then
 			fail "invalid VM configuration syntax $vm_conf"
 		fi