# UNDF: UNDF-2026-000000265
diff --git a/vm_args.c b/vm_args.c
--- a/vm_args.c
+++ b/vm_args.c
@@ -299,30 +299,50 @@ static inline int
-args_setup_kw_parameters_lookup(const ID key, VALUE *ptr,
-        const VALUE *const passed_keywords, VALUE *passed_values,
-        const int passed_keyword_len)
-{
-    int i;
-    const VALUE keyname = ID2SYM(key);
-
-    for (i=0; i<passed_keyword_len; i++) {   /* O(passed_keyword_len) */
-        if (keyname == passed_keywords[i]) {
-            *ptr = passed_values[i];
-            passed_values[i] = Qundef;
-            return TRUE;
-        }
-    }
-
-    return FALSE;
-}
+/* Build a temporary st_table from passed keyword symbol -> value-slot index.
+ * Replaces O(K * P) double-loop with O(K + P): one pass to build the map,
+ * one O(1) lookup per accepted keyword.
+ */
+static st_table *
+build_passed_kw_table(const VALUE *const passed_keywords,
+                      const int passed_keyword_len)
+{
+    st_table *tbl = st_init_numtable_with_size(passed_keyword_len);
+    for (int i = 0; i < passed_keyword_len; i++) {
+        st_insert(tbl, (st_data_t)passed_keywords[i], (st_data_t)i);
+    }
+    return tbl;
+}

 static void
 args_setup_kw_parameters(rb_execution_context_t *const ec, const rb_iseq_t *const iseq, const rb_callable_method_entry_t *cme,
                          VALUE *const passed_values, const int passed_keyword_len, const VALUE *const passed_keywords,
                          VALUE *const locals)
 {
     const ID *acceptable_keywords = ISEQ_BODY(iseq)->param.keyword->table;
     const int req_key_num = ISEQ_BODY(iseq)->param.keyword->required_num;
     const int key_num = ISEQ_BODY(iseq)->param.keyword->num;
     const VALUE * const default_values = ISEQ_BODY(iseq)->param.keyword->default_values;
     VALUE missing = 0;
     int i, di, found = 0;
     int unspecified_bits = 0;
     VALUE unspecified_bits_value = Qnil;

+    /* Build O(1) lookup map once — replaces O(K*P) nested loop */
+    st_table *kw_map = (passed_keyword_len > 0)
+        ? build_passed_kw_table(passed_keywords, passed_keyword_len)
+        : NULL;
+
     for (i=0; i<req_key_num; i++) {
         ID key = acceptable_keywords[i];
-        if (args_setup_kw_parameters_lookup(key, &locals[i], passed_keywords, passed_values, passed_keyword_len)) {
+        VALUE keyname = ID2SYM(key);
+        st_data_t idx;
+        if (kw_map && st_lookup(kw_map, (st_data_t)keyname, &idx)) {
+            locals[i] = passed_values[idx];
+            passed_values[idx] = Qundef;
             found++;
-        }
-        else {
+        } else {
             if (!missing) missing = rb_ary_hidden_new(1);
             rb_ary_push(missing, ID2SYM(key));
         }
     }

     if (missing) argument_kw_error(ec, iseq, cme, "missing", missing);

     for (di=0; i<key_num; i++, di++) {
-        if (args_setup_kw_parameters_lookup(acceptable_keywords[i], &locals[i], passed_keywords, passed_values, passed_keyword_len)) {
+        VALUE keyname = ID2SYM(acceptable_keywords[i]);
+        st_data_t idx;
+        if (kw_map && st_lookup(kw_map, (st_data_t)keyname, &idx)) {
+            locals[i] = passed_values[idx];
+            passed_values[idx] = Qundef;
             found++;
-        }
-        else {
+        } else {