diff --git a/openwrt/files/luci/model/cbi/ua3f/fields.lua b/openwrt/files/luci/model/cbi/ua3f/fields.lua
index 25f38d6..7f03cff 100644
--- a/openwrt/files/luci/model/cbi/ua3f/fields.lua
+++ b/openwrt/files/luci/model/cbi/ua3f/fields.lua
@@ -11,15 +11,19 @@ local ListValue = cbi.ListValue
 local DummyValue = cbi.DummyValue
 local TextValue = cbi.TextValue
 
+function cmd_exists(cmd)
+    return sys.call("command -v " .. cmd .. " >/dev/null 2>&1") == 0
+end
+
 function nfqueue_exists()
-    local opkg = sys.call("opkg list-installed kmod-nft-queue | grep -q kmod-nft-queue") == 0
-    local apk = sys.call("apk info | grep -q kmod-nft-queue") == 0
+    local opkg = cmd_exists("opkg") and sys.call("opkg list-installed kmod-nft-queue | grep -q kmod-nft-queue") == 0
+    local apk = cmd_exists("apk") and (sys.call("apk info | grep -q kmod-nft-queue") == 0)
     return opkg or apk
 end
 
 function tproxy_exists()
-    local opkg = sys.call("opkg list-installed kmod-nft-tproxy | grep -q kmod-nft-tproxy") == 0
-    local apk = sys.call("apk info | grep -q kmod-nft-tproxy") == 0
+    local opkg = cmd_exists("opkg") and sys.call("opkg list-installed kmod-nft-tproxy | grep -q kmod-nft-tproxy") == 0
+    local apk = cmd_exists("apk") and (sys.call("apk info | grep -q kmod-nft-tproxy") == 0)
     return opkg or apk
 end