diff --git a/scripts/lua/macs_stats.lua b/scripts/lua/macs_stats.lua
index 00542d8c11..5b6f513fa8 100644
--- a/scripts/lua/macs_stats.lua
+++ b/scripts/lua/macs_stats.lua
@@ -81,7 +81,7 @@ if((devices_mode == "inactive_macs_only") and ntop.isEnterpriseL()) then
       if(active_macs[mac] == None) then
         local m = get_manufacturer_mac(mac)
 
-        if(m ~= "") then
+        if not isEmptyString(m) then
          if(manufacturers[m] == None) then
            manufacturers[m] = 1
          else
diff --git a/scripts/lua/modules/lua_utils_get.lua b/scripts/lua/modules/lua_utils_get.lua
index fa6d06f2be..44b64ee4f0 100644
--- a/scripts/lua/modules/lua_utils_get.lua
+++ b/scripts/lua/modules/lua_utils_get.lua
@@ -683,15 +683,15 @@ function get_manufacturer_mac(mac_address)
    local m = string.sub(mac_address, 1, 8)
    local ret = get_mac_classification(m, true --[[ extended name --]] )
 
-   if (ret == m) then
-      ret = "n/a"
+   if ret == m then
+      ret = ""
    end
 
-   if ret and ret ~= "" then
+   if not isEmptyString(ret) then
       ret = ret:gsub("'", " ")
    end
 
-   return ret or "n/a"
+   return ret
 end
 
 -- ##############################################
diff --git a/scripts/lua/modules/lua_utils_gui.lua b/scripts/lua/modules/lua_utils_gui.lua
index acc64fe64f..4a6f8f5bda 100644
--- a/scripts/lua/modules/lua_utils_gui.lua
+++ b/scripts/lua/modules/lua_utils_gui.lua
@@ -489,7 +489,12 @@ local guess_icon_keys = {
 -- #############################################
 
 function guessHostIcon(key)
-    local m = string.lower(get_manufacturer_mac(key))
+    local m = get_manufacturer_mac(key)
+    if isEmptyString(m) then
+        return ""
+    end
+
+    m = string.lower(get_manufacturer_mac(key))
     local icon = guess_icon_keys[m]
 
     if ((icon ~= nil) and (icon ~= "")) then