diff --git a/test/lib/aux.sh b/test/lib/aux.sh
index 20a8a1e45..93345bf12 100644
--- a/test/lib/aux.sh
+++ b/test/lib/aux.sh
@@ -475,7 +475,7 @@ teardown_devs() {
 	rm -f DEVICES LOOP
 
 	# Attempt to remove any loop devices that failed to get torn down if earlier tests aborted
-	test "${LVM_TEST_PARALLEL:-0}" -eq 1 -o -z "$COMMON_PREFIX" || {
+	test "${LVM_TEST_PARALLEL:-0}" -eq 1 || test -z "$COMMON_PREFIX" || {
 		local stray_loops=( $(losetup -a | grep "$COMMON_PREFIX" | cut -d: -f1) )
 		test ${#stray_loops[@]} -eq 0 || {
 			teardown_devs_prefixed "$COMMON_PREFIX" 1
@@ -678,7 +678,7 @@ prepare_loop() {
 # - scripts must take care not to use a DEV_SIZE that will enduce OOM-killer
 prepare_scsi_debug_dev() {
 	local DEV_SIZE=$1
-	local SCSI_DEBUG_PARAMS=( ${@:2} )
+	shift # rest of params directly passed to modprobe
 	local DEBUG_DEV
 
 	rm -f debug.log strace.log
@@ -694,7 +694,7 @@ prepare_scsi_debug_dev() {
 	# NOTE: it will _never_ make sense to pass num_tgts param;
 	# last param wins.. so num_tgts=1 is imposed
 	touch SCSI_DEBUG_DEV
-	modprobe scsi_debug dev_size_mb="$DEV_SIZE" "${SCSI_DEBUG_PARAMS[@]}" num_tgts=1 || skip
+	modprobe scsi_debug dev_size_mb="$DEV_SIZE" "$@" num_tgts=1 || skip
 
 	for i in {1..20} ; do
 		DEBUG_DEV="/dev/$(grep -H scsi_debug /sys/block/*/device/model | cut -f4 -d /)"
@@ -1159,7 +1159,7 @@ devices/cache_dir = "$TESTDIR/etc"
 devices/default_data_alignment = 1
 devices/dir = "$DM_DEV_DIR"
 devices/filter = "a|.*|"
-devices/global_filter = [ "a|$DM_DEV_DIR/mapper/.*pv[0-9_]*$|", "r|.*|" ]
+devices/global_filter = [ "a|$DM_DEV_DIR/mapper/${PREFIX}.*pv[0-9_]*$|", "r|.*|" ]
 devices/md_component_detection  = 0
 devices/scan = "$DM_DEV_DIR"
 devices/sysfs_scan = 1