diff --git a/binding/lua_c/bench_test.lua b/binding/lua_c/bench_test.lua
index 82b7583..b43391b 100644
--- a/binding/lua_c/bench_test.lua
+++ b/binding/lua_c/bench_test.lua
@@ -40,6 +40,9 @@ for _, r in ipairs(arg) do
             srcFile = v
         elseif k == "cache-policy" then
             cachePolicy = v
+        else
+            print(string.format("undefined option `%s`", r))
+            return
         end
 
         -- break the match iterate
diff --git a/binding/lua_c/search_test.lua b/binding/lua_c/search_test.lua
index 21627c4..41949d1 100644
--- a/binding/lua_c/search_test.lua
+++ b/binding/lua_c/search_test.lua
@@ -37,6 +37,9 @@ for _, r in ipairs(arg) do
             dbFile = v
         elseif k == "cache-policy" then
             cachePolicy = v
+        else
+            print(string.format("undefined option `%s`", r))
+            return
         end
 
         -- break the match iterate