diff --git a/userspace/lib/ygglibc/src/headers/wchar/multibyte.rs b/userspace/lib/ygglibc/src/headers/wchar/multibyte.rs
index 69241815..350adb79 100644
--- a/userspace/lib/ygglibc/src/headers/wchar/multibyte.rs
+++ b/userspace/lib/ygglibc/src/headers/wchar/multibyte.rs
@@ -1,20 +1,41 @@
-use core::{ffi::{c_char, c_int}, ptr::NonNull};
+use core::{
+    ffi::{c_char, c_int},
+    ptr::NonNull,
+};
 
-use crate::{error::CUsizeResult, headers::wchar::imp, types::wchar_t};
+use crate::{
+    error::{CIntZeroResult, CUsizeResult, OptionExt},
+    headers::{errno::Errno, stdlib::MB_CUR_MAX, wchar::imp},
+    types::wchar_t,
+    util::PointerExt,
+};
 
 use super::mbstate_t;
 
+static mut GLOBAL: mbstate_t = mbstate_t { __dummy: 0 };
+
 #[no_mangle]
 unsafe extern "C" fn mbrlen(_str: *const c_char, _n: usize, _state: *mut mbstate_t) -> usize {
     todo!()
 }
 
 #[no_mangle]
-unsafe extern "C" fn wcrtomb(_dst: *mut c_char, _wc: wchar_t, _state: *mut mbstate_t) -> usize {
-    todo!()
+unsafe extern "C" fn wcrtomb(dst: *mut c_char, wc: wchar_t, state: *mut mbstate_t) -> CUsizeResult {
+    let state = match state.as_mut() {
+        Some(state) => state,
+        #[allow(static_mut_refs)]
+        None => &mut GLOBAL,
+    };
+    // dst must be at least MB_CUR_MAX (4)
+    let dst = dst.cast::<u8>().ensure_slice_mut(MB_CUR_MAX as usize);
+
+    // TODO EILSEQ
+    let ch = char::from_u32(wc as u32).e_ok_or(Errno::EINVAL)?;
+
+    let len = ch.encode_utf8(dst).len();
+    CUsizeResult::success(len)
 }
 
-#[allow(static_mut_refs)]
 #[no_mangle]
 pub unsafe extern "C" fn mbrtowc(
     dst: *mut wchar_t,
@@ -22,17 +43,14 @@ pub unsafe extern "C" fn mbrtowc(
     n: usize,
     state: *mut mbstate_t,
 ) -> CUsizeResult {
-    static mut GLOBAL: mbstate_t = mbstate_t { __dummy: 0 };
-
     let state = match state.as_mut() {
         Some(state) => state,
-        None => &mut GLOBAL
+        #[allow(static_mut_refs)]
+        None => &mut GLOBAL,
     };
 
     let res = match NonNull::new(src.cast_mut()) {
-        Some(src) => {
-            imp::mbrtowc(dst, src, n, state)?
-        }
+        Some(src) => imp::mbrtowc(dst, src, n, state)?,
         None => {
             let x: [c_char; 1] = [0];
             imp::mbrtowc(dst, NonNull::from_ref(&x[0]), 1, state)?
@@ -43,8 +61,8 @@ pub unsafe extern "C" fn mbrtowc(
 }
 
 #[no_mangle]
-unsafe extern "C" fn mbsinit(_state: *const mbstate_t) -> c_int {
-    todo!()
+unsafe extern "C" fn mbsinit(_state: *const mbstate_t) -> CIntZeroResult {
+    CIntZeroResult::SUCCESS
 }
 
 #[no_mangle]