diff --git a/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua b/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua
index 53e8e18..911969c 100644
--- a/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua
+++ b/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua
@@ -27,7 +27,7 @@ function wifi.invert_rx_tx(interface)
 end
 
 function wifi.parse_hostapd_clients(clients,exclude_mac)
-  local data = {}
+  local data
   for mac, properties in pairs(clients) do
     if not exclude_mac[mac] then
       properties.mac = mac
@@ -38,7 +38,7 @@ function wifi.parse_hostapd_clients(clients,exclude_mac)
 end
 
 function wifi.parse_iwinfo_clients(clients,exclude_mac)
-  local data = {}
+  local data
   for _, p in pairs(clients) do
     if not exclude_mac[p.mac] then
       local client = {}