diff --git a/utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/openwrt.lua b/utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/openwrt.lua
index 8d44792b9..a92b7ddc1 100644
--- a/utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/openwrt.lua
+++ b/utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/openwrt.lua
@@ -12,9 +12,9 @@ local labels = {
     target = b.release.target
 }
 
-b = nil
-u = nil
-ubus = nil
+local b = nil
+local u = nil
+local ubus = nil
 
 local function scrape()
     metric("node_openwrt_info", "gauge", labels, 1)