diff --git a/nac3artiq/demo/rpc_kwargs_test.py b/nac3artiq/demo/rpc_kwargs_test.py
new file mode 100644
index 00000000..d4a444b2
--- /dev/null
+++ b/nac3artiq/demo/rpc_kwargs_test.py
@@ -0,0 +1,37 @@
+from min_artiq import *
+from numpy import int32
+
+@rpc
+def sum_3(a: int32, b: int32 = 10, c: int32 = 20) -> int32:
+    """
+    An RPC function to test NAC3's handling of positional/keyword arguments.
+    """
+    return int32(a + b + c)
+
+@nac3
+class RpcKwargTest:
+    core: KernelInvariant[Core]
+
+    def __init__(self):
+        self.core = Core()
+
+    @kernel
+    def run(self):
+        #1) All positional => a=1, b=2, c=3 -> total=6
+        s1 = sum_3(1, 2, 3)
+        assert s1 == 6
+
+        #2) Use the default b=10, c=20 => a=5 => total=35
+        s2 = sum_3(5)
+        assert s2 == 35
+
+        #3) a=1 (positional), b=100 (keyword), omit c => c=20 => total=121
+        s3 = sum_3(1, b=100)
+        assert s3 == 121
+
+        #4) a=2, c=300 => b=10 (default) => total=312
+        s4 = sum_3(a=2, c=300)
+        assert s4 == 312
+
+if __name__ == "__main__":
+    RpcKwargTest().run()
\ No newline at end of file
diff --git a/nac3artiq/src/codegen.rs b/nac3artiq/src/codegen.rs
index cc625a02..34ae43f7 100644
--- a/nac3artiq/src/codegen.rs
+++ b/nac3artiq/src/codegen.rs
@@ -1,5 +1,5 @@
 use std::{
-    collections::{hash_map::DefaultHasher, HashMap},
+    collections::hash_map::DefaultHasher,
     hash::{Hash, Hasher},
     iter::once,
     mem,
@@ -43,7 +43,9 @@ use nac3core::{
     },
     typecheck::{
         type_inferencer::PrimitiveStore,
-        typedef::{iter_type_vars, FunSignature, FuncArg, Type, TypeEnum, VarMap},
+        typedef::{
+        iter_type_vars, FunSignature, FuncArg, Type, TypeEnum, TypeEnum::*, VarMap,
+    },
     },
 };
 
@@ -83,8 +85,8 @@ pub struct ArtiqCodeGenerator<'a> {
 
     /// The [`ParallelMode`] of the current parallel context.
     ///
-    /// The current parallel context refers to the nearest `with parallel` or `with legacy_parallel`
-    /// statement, which is used to determine when and how the timeline should be updated.
+    /// The current parallel context refers to the nearest `with` statement,
+    /// which is used to determine when and how the timeline should be updated.
     parallel_mode: ParallelMode,
 
     /// Specially treated python IDs to identify `with parallel` and `with sequential` blocks.
@@ -412,9 +414,12 @@ impl CodeGenerator for ArtiqCodeGenerator<'_> {
 fn gen_rpc_tag(
     ctx: &mut CodeGenContext<'_, '_>,
     ty: Type,
+    is_kwarg: bool,
     buffer: &mut Vec<u8>,
 ) -> Result<(), String> {
-    use nac3core::typecheck::typedef::TypeEnum::*;
+    if is_kwarg {
+        buffer.push(b'k');
+    }
 
     let PrimitiveStore { int32, int64, float, bool, str, none, .. } = ctx.primitives;
 
@@ -437,14 +442,14 @@ fn gen_rpc_tag(
                 buffer.push(b't');
                 buffer.push(ty.len() as u8);
                 for ty in ty {
-                    gen_rpc_tag(ctx, *ty, buffer)?;
+                    gen_rpc_tag(ctx, *ty, false, buffer)?;
                 }
             }
             TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
                 let ty = iter_type_vars(params).next().unwrap().ty;
 
                 buffer.push(b'l');
-                gen_rpc_tag(ctx, ty, buffer)?;
+                gen_rpc_tag(ctx, ty, false, buffer)?;
             }
             TObj { obj_id, .. } if *obj_id == PrimDef::NDArray.id() => {
                 let (ndarray_dtype, ndarray_ndims) = unpack_ndarray_var_tys(&mut ctx.unifier, ty);
@@ -468,7 +473,7 @@ fn gen_rpc_tag(
 
                 buffer.push(b'a');
                 buffer.push((ndarray_ndims & 0xFF) as u8);
-                gen_rpc_tag(ctx, ndarray_dtype, buffer)?;
+                gen_rpc_tag(ctx, ndarray_dtype, false, buffer)?;
             }
             _ => return Err(format!("Unsupported type: {:?}", ctx.unifier.stringify(ty))),
         }
@@ -833,106 +838,119 @@ fn rpc_codegen_callback_fn<'ctx>(
     let int32 = ctx.ctx.i32_type();
     let size_type = ctx.get_size_type();
     let ptr_type = int8.ptr_type(AddressSpace::default());
-    let tag_ptr_type = ctx.ctx.struct_type(&[ptr_type.into(), size_type.into()], false);
-
     let service_id = int32.const_int(fun.1 .0 as u64, false);
     // -- setup rpc tags
     let mut tag = Vec::new();
     if obj.is_some() {
         tag.push(b'O');
     }
-    for arg in &fun.0.args {
-        gen_rpc_tag(ctx, arg.ty, &mut tag)?;
+    for param in &fun.0.args {
+        gen_rpc_tag(ctx, param.ty, false, &mut tag)?;
     }
     tag.push(b':');
-    gen_rpc_tag(ctx, fun.0.ret, &mut tag)?;
+    gen_rpc_tag(ctx, fun.0.ret, false, &mut tag)?;
 
     let mut hasher = DefaultHasher::new();
     tag.hash(&mut hasher);
-    let hash = format!("{}", hasher.finish());
+    let hash = format!("rpc_tag_{}", hasher.finish());
 
-    let tag_ptr = ctx
-        .module
-        .get_global(hash.as_str())
-        .unwrap_or_else(|| {
-            let tag_arr_ptr = ctx.module.add_global(
-                int8.array_type(tag.len() as u32),
-                None,
-                format!("tagptr{}", fun.1 .0).as_str(),
-            );
-            tag_arr_ptr.set_initializer(&int8.const_array(
-                &tag.iter().map(|v| int8.const_int(u64::from(*v), false)).collect::<Vec<_>>(),
-            ));
-            tag_arr_ptr.set_linkage(Linkage::Private);
-            let tag_ptr = ctx.module.add_global(tag_ptr_type, None, &hash);
-            tag_ptr.set_linkage(Linkage::Private);
-            tag_ptr.set_initializer(&ctx.ctx.const_struct(
-                &[
-                    tag_arr_ptr.as_pointer_value().const_cast(ptr_type).into(),
-                    size_type.const_int(tag.len() as u64, false).into(),
-                ],
-                false,
-            ));
-            tag_ptr
-        })
-        .as_pointer_value();
+    let maybe_existing = ctx.module.get_global(&hash);
+    let tag_ptr = if let Some(gv) = maybe_existing {
+        gv.as_pointer_value()
+    } else {
+        let tag_len = tag.len();
+        let arr_ty = int8.array_type(tag_len as u32);
+        let tag_const = int8
+            .const_array(&tag.iter().map(|&b| int8.const_int(u64::from(b), false)).collect_vec());
+        let arr_gv = ctx.module.add_global(arr_ty, None, &format!("{hash}.arr"));
+        arr_gv.set_linkage(Linkage::Private);
+        arr_gv.set_initializer(&tag_const);
 
-    let arg_length = args.len() + usize::from(obj.is_some());
+        let st = ctx.ctx.const_struct(
+            &[
+                arr_gv.as_pointer_value().const_cast(ptr_type).into(),
+                size_type.const_int(tag_len as u64, false).into(),
+            ],
+            false,
+        );
+        let st_gv = ctx.module.add_global(st.get_type(), None, &hash);
+        st_gv.set_linkage(Linkage::Private);
+        st_gv.set_initializer(&st);
 
-    let stackptr = call_stacksave(ctx, Some("rpc.stack"));
-    let args_ptr = ctx
-        .builder
-        .build_array_alloca(
-            ptr_type,
-            ctx.ctx.i32_type().const_int(arg_length as u64, false),
-            "argptr",
-        )
-        .unwrap();
+        st_gv.as_pointer_value()
+    };
 
-    // -- rpc args handling
-    let mut keys = fun.0.args.clone();
-    let mut mapping = HashMap::new();
-    for (key, value) in args {
-        mapping.insert(key.unwrap_or_else(|| keys.remove(0).name), value);
+    let n_params = fun.0.args.len();
+    let mut param_map: Vec<Option<ValueEnum<'ctx>>> = vec![None; n_params];
+
+    let mut pos_index = 0usize;
+
+    if let Some((_obj_ty, obj_val)) = obj {
+        param_map[0] = Some(obj_val);
+        pos_index = 1;
     }
-    // default value handling
-    for k in keys {
-        mapping
-            .insert(k.name, ctx.gen_symbol_val(generator, &k.default_value.unwrap(), k.ty).into());
-    }
-    // reorder the parameters
-    let mut real_params = fun
-        .0
-        .args
-        .iter()
-        .map(|arg| {
-            mapping
-                .remove(&arg.name)
-                .unwrap()
-                .to_basic_value_enum(ctx, generator, arg.ty)
-                .map(|llvm_val| (llvm_val, arg.ty))
-        })
-        .collect::<Result<Vec<(_, _)>, _>>()?;
-    if let Some(obj) = obj {
-        if let ValueEnum::Static(obj_val) = obj.1 {
-            real_params.insert(0, (obj_val.get_const_obj(ctx, generator), obj.0));
+    for (maybe_key, val_enum) in args {
+        if let Some(kw_name) = maybe_key {
+            let param_pos = fun
+                .0
+                .args
+                .iter()
+                .position(|arg| arg.name == kw_name)
+                .ok_or_else(|| format!("Unknown keyword argument '{kw_name}'"))?;
+
+            if param_map[param_pos].is_some() {
+                return Err(format!("Multiple values for argument '{kw_name}'"));
+            }
+            param_map[param_pos] = Some(val_enum);
         } else {
-            // should be an error here...
-            panic!("only host object is allowed");
+            while pos_index < n_params && param_map[pos_index].is_some() {
+                pos_index += 1;
+            }
+            if pos_index >= n_params {
+                return Err("Too many positional arguments given to function.".to_string());
+            }
+            param_map[pos_index] = Some(val_enum);
+            pos_index += 1;
         }
     }
 
-    for (i, (arg, arg_ty)) in real_params.iter().enumerate() {
-        let arg_slot = format_rpc_arg(generator, ctx, (*arg, *arg_ty, i));
-        let arg_ptr = unsafe {
+    for (i, param) in fun.0.args.iter().enumerate() {
+        if param_map[i].is_none() {
+            if let Some(default_expr) = &param.default_value {
+                let default_val = ctx.gen_symbol_val(generator, default_expr, param.ty).into();
+                param_map[i] = Some(default_val);
+            } else {
+                return Err(format!("Missing required argument '{}'", param.name));
+            }
+        }
+    }
+    let mut real_params = Vec::with_capacity(n_params);
+    for (i, param_spec) in fun.0.args.iter().enumerate() {
+        let some_valenum = param_map[i].take().unwrap();
+        let llvm_val = some_valenum.to_basic_value_enum(ctx, generator, param_spec.ty)?;
+        real_params.push((llvm_val, param_spec.ty));
+    }
+
+    let arg_count = real_params.len() as u64;
+    let stackptr = call_stacksave(ctx, Some("rpc.stack"));
+
+    let i32_ty = ctx.ctx.i32_type();
+    let arg_array = ctx
+        .builder
+        .build_array_alloca(ptr_type, i32_ty.const_int(arg_count, false), "rpc.arg_array")
+        .unwrap();
+
+    for (i, (llvm_val, ty)) in real_params.iter().enumerate() {
+        let arg_slot_ptr = unsafe {
             ctx.builder.build_gep(
-                args_ptr,
-                &[int32.const_int(i as u64, false)],
-                &format!("rpc.arg{i}"),
+                arg_array,
+                &[i32_ty.const_int(i as u64, false)],
+                &format!("rpc.arg_slot_{i}"),
             )
         }
         .unwrap();
-        ctx.builder.build_store(arg_ptr, arg_slot).unwrap();
+        let arg_ptr = format_rpc_arg(generator, ctx, (*llvm_val, *ty, i));
+        ctx.builder.build_store(arg_slot_ptr, arg_ptr).unwrap();
     }
 
     // call
@@ -940,7 +958,7 @@ fn rpc_codegen_callback_fn<'ctx>(
         ctx,
         if is_async { "rpc_send_async" } else { "rpc_send" },
         None,
-        &[service_id.into(), tag_ptr.into(), args_ptr.into()],
+        &[service_id.into(), tag_ptr.into(), arg_array.into()],
         Some("rpc.send"),
         None,
     );
@@ -948,19 +966,8 @@ fn rpc_codegen_callback_fn<'ctx>(
     // reclaim stack space used by arguments
     call_stackrestore(ctx, stackptr);
 
-    if is_async {
-        // async RPCs do not return any values
-        Ok(None)
-    } else {
-        let result = format_rpc_ret(generator, ctx, fun.0.ret);
-
-        if !result.is_some_and(|res| res.get_type().is_pointer_type()) {
-            // An RPC returning an NDArray would not touch here.
-            call_stackrestore(ctx, stackptr);
-        }
-
-        Ok(result)
-    }
+    let maybe_ret = format_rpc_ret(generator, ctx, fun.0.ret);
+    Ok(maybe_ret)
 }
 
 pub fn attributes_writeback<'ctx>(
@@ -1008,7 +1015,7 @@ pub fn attributes_writeback<'ctx>(
                         if !is_mutable {
                             continue;
                         }
-                        if gen_rpc_tag(ctx, *field_ty, &mut scratch_buffer).is_ok() {
+                        if gen_rpc_tag(ctx, *field_ty, false, &mut scratch_buffer).is_ok() {
                             attributes.push(name.to_string());
                             let (index, _) = ctx.get_attr_index(ty, *name);
                             values.push((
@@ -1031,7 +1038,7 @@ pub fn attributes_writeback<'ctx>(
                 TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
                     let elem_ty = iter_type_vars(params).next().unwrap().ty;
 
-                    if gen_rpc_tag(ctx, elem_ty, &mut scratch_buffer).is_ok() {
+                    if gen_rpc_tag(ctx, elem_ty, false, &mut scratch_buffer).is_ok() {
                         let pydict = PyDict::new(py);
                         pydict.set_item("obj", val)?;
                         host_attributes.append(pydict)?;
@@ -1049,7 +1056,7 @@ pub fn attributes_writeback<'ctx>(
                         if *is_method {
                             continue;
                         }
-                        if gen_rpc_tag(ctx, *field_ty, &mut scratch_buffer).is_ok() {
+                        if gen_rpc_tag(ctx, *field_ty, false, &mut scratch_buffer).is_ok() {
                             fields.push(name.to_string());
                             let (index, _) = ctx.get_attr_index(ty, *name);
                             values.push((