diff --git a/include/pocketpy/codeobject.h b/include/pocketpy/codeobject.h
index 9ad1df12..e02920e7 100644
--- a/include/pocketpy/codeobject.h
+++ b/include/pocketpy/codeobject.h
@@ -138,10 +138,13 @@ struct FuncDecl {
     Str docstring;              // docstring of this function
     bool is_simple;
 
-    int keyword_to_index(StrName key) const{
-        for(const KwArg& item: kwargs) if(item.key == key) return item.index;
-        return -1;
+    NameDictInt kw_to_index;
+
+    void add_kwarg(int index, StrName key, PyObject* value){
+        kw_to_index.set(key, index);
+        kwargs.push_back({index, key, value});
     }
+    
     void _gc_mark() const;
 };
 
diff --git a/src/compiler.cpp b/src/compiler.cpp
index 36d94219..7286b0ab 100644
--- a/src/compiler.cpp
+++ b/src/compiler.cpp
@@ -1037,7 +1037,7 @@ __EAT_DOTS_END:
                     if(value == nullptr){
                         SyntaxError(Str("default argument must be a literal"));
                     }
-                    decl->kwargs.push_back(FuncDecl::KwArg{index, name, value});
+                    decl->add_kwarg(index, name, value);
                 } break;
                 case 3:
                     decl->starred_kwarg = index;
diff --git a/src/vm.cpp b/src/vm.cpp
index 595c3a5c..0b586eff 100644
--- a/src/vm.cpp
+++ b/src/vm.cpp
@@ -844,9 +844,9 @@ void VM::_prepare_py_call(PyObject** buffer, ArgsView args, ArgsView kwargs, con
 
     for(int j=0; j<kwargs.size(); j+=2){
         StrName key(CAST(int, kwargs[j]));
-        int index = decl->keyword_to_index(key);
+        int index = decl->kw_to_index.try_get_likely_found(key);
         // if key is an explicit key, set as local variable
-        if(index != -1){
+        if(index >= 0){
             buffer[index] = kwargs[j+1];
         }else{
             // otherwise, set as **kwargs if possible