diff --git a/plugins/zfs/zpool_iostat b/plugins/zfs/zpool_iostat
index 34e0ec20..63400422 100755
--- a/plugins/zfs/zpool_iostat
+++ b/plugins/zfs/zpool_iostat
@@ -102,14 +102,14 @@ if [ "$ACTION" = "config" ]; then
 	# each device.
 	printf "graph_order"
 	echo "$zlist" | while read -r device_id; do
-		fieldname="$(get_device_fieldname "pool_$device_id")"
+		fieldname="$(get_device_fieldname "$device_id")"
 		printf " %s_read %s_write" "$fieldname" "$fieldname"
 	done
 	# finalize the 'graph_order' with a newline
 	echo
 	# output all fields: write as negative numbers and read as positive
 	echo "$zlist" | while read -r device_id; do
-		fieldname="$(get_device_fieldname "pool_$device_id")"
+		fieldname="$(get_device_fieldname "$device_id")"
 		echo "${fieldname}_read.label $device_id"
 		echo "${fieldname}_read.type GAUGE"
 		echo "${fieldname}_read.graph no"
@@ -122,7 +122,7 @@ fi
 
 
 echo "$zlist" | while read -r device_id; do
-	fieldname="$(get_device_fieldname "pool_$device_id")"
+	fieldname="$(get_device_fieldname "$device_id")"
 	echo "${fieldname}_read.value $(get_device_iostat_column "$device_id" 6)"
 	echo "${fieldname}_write.value $(get_device_iostat_column "$device_id" 7)"
 done