diff --git a/crates/lune-std-ffi/src/c/fn_info.rs b/crates/lune-std-ffi/src/c/fn_info.rs
index 3c701a5..1fe4ec7 100644
--- a/crates/lune-std-ffi/src/c/fn_info.rs
+++ b/crates/lune-std-ffi/src/c/fn_info.rs
@@ -93,6 +93,10 @@ impl CFnInfo {
         arg_table: LuaTable,
         ret: LuaAnyUserData,
     ) -> LuaResult<LuaAnyUserData<'lua>> {
+        if helper::has_void(&arg_table)? {
+            return Err(LuaError::external("Arguments can not include void type"));
+        }
+
         let args_types = helper::get_middle_type_list(&arg_table)?;
         let ret_type = helper::get_middle_type(&ret)?;
 
diff --git a/crates/lune-std-ffi/src/c/helper.rs b/crates/lune-std-ffi/src/c/helper.rs
index 8a22a5b..7f452fe 100644
--- a/crates/lune-std-ffi/src/c/helper.rs
+++ b/crates/lune-std-ffi/src/c/helper.rs
@@ -211,6 +211,7 @@ pub unsafe fn get_conv(userdata: &LuaAnyUserData) -> LuaResult<*const dyn FfiCon
     }
 }
 
+// Create vec<T> from table with (userdata)->T
 pub fn create_list<T>(
     table: &LuaTable,
     callback: fn(&LuaAnyUserData) -> LuaResult<T>,
@@ -226,10 +227,12 @@ pub fn create_list<T>(
     Ok(list)
 }
 
+//Get
 pub unsafe fn get_conv_list(table: &LuaTable) -> LuaResult<Vec<*const dyn FfiConvert>> {
     create_list(table, |userdata| get_conv(userdata))
 }
 
+// Get type size from ctype userdata
 pub fn get_size(userdata: &LuaAnyUserData) -> LuaResult<usize> {
     if userdata.is::<CStructInfo>() {
         Ok(userdata.borrow::<CStructInfo>()?.get_size())
@@ -244,7 +247,7 @@ pub fn get_size(userdata: &LuaAnyUserData) -> LuaResult<usize> {
     }
 }
 
-// get libffi_type from any c-type userdata
+// Get libffi_type from ctype userdata
 pub fn get_middle_type(userdata: &LuaAnyUserData) -> LuaResult<Type> {
     if userdata.is::<CStructInfo>() {
         Ok(userdata.borrow::<CStructInfo>()?.get_middle_type())
@@ -274,6 +277,16 @@ pub fn get_middle_type_list(table: &LuaTable) -> LuaResult<Vec<Type>> {
     create_list(table, get_middle_type)
 }
 
+pub fn has_void(table: &LuaTable) -> LuaResult<bool> {
+    for i in 0..table.raw_len() {
+        let value: LuaValue = table.raw_get(i + 1)?;
+        if get_userdata(value)?.is::<CVoidInfo>() {
+            return Ok(false);
+        }
+    }
+    Ok(false)
+}
+
 // stringify any c-type userdata (for recursive)
 pub fn stringify(lua: &Lua, userdata: &LuaAnyUserData) -> LuaResult<String> {
     if userdata.is::<CStructInfo>() {
diff --git a/crates/lune-std-ffi/src/c/mod.rs b/crates/lune-std-ffi/src/c/mod.rs
index c2cdbc3..ffd4562 100644
--- a/crates/lune-std-ffi/src/c/mod.rs
+++ b/crates/lune-std-ffi/src/c/mod.rs
@@ -15,6 +15,7 @@ pub use self::{
     struct_info::CStructInfo,
     type_info::{CTypeCast, CTypeInfo},
     types::{ctype_helper, export_ctypes},
+    void_info::CVoidInfo,
 };
 
 // Named registry table names
diff --git a/crates/lune-std-ffi/src/c/struct_info.rs b/crates/lune-std-ffi/src/c/struct_info.rs
index 9430a2f..1e52e36 100644
--- a/crates/lune-std-ffi/src/c/struct_info.rs
+++ b/crates/lune-std-ffi/src/c/struct_info.rs
@@ -65,6 +65,10 @@ impl CStructInfo {
         lua: &'lua Lua,
         table: LuaTable<'lua>,
     ) -> LuaResult<LuaAnyUserData<'lua>> {
+        if helper::has_void(&table)? {
+            return Err(LuaError::external("Void field in sturct is not allowed"));
+        }
+
         let cstruct = lua
             .create_userdata(Self::new(helper::get_middle_type_list(&table)?, unsafe {
                 helper::get_conv_list(&table)?
diff --git a/crates/lune-std-ffi/src/c/void_info.rs b/crates/lune-std-ffi/src/c/void_info.rs
index 6d70081..0d36a35 100644
--- a/crates/lune-std-ffi/src/c/void_info.rs
+++ b/crates/lune-std-ffi/src/c/void_info.rs
@@ -16,6 +16,9 @@ impl FfiSize for CVoidInfo {
     }
 }
 impl CVoidInfo {
+    pub fn new() -> Self {
+        Self()
+    }
     pub fn get_middle_type() -> Type {
         Type::void()
     }
diff --git a/crates/lune-std-ffi/src/data/callable_data.rs b/crates/lune-std-ffi/src/data/callable_data.rs
index d5c9bd8..8a3f6ac 100644
--- a/crates/lune-std-ffi/src/data/callable_data.rs
+++ b/crates/lune-std-ffi/src/data/callable_data.rs
@@ -1,5 +1,5 @@
 use core::ffi::c_void;
-use std::cell::Ref;
+use std::ptr;
 
 use libffi::{
     low::{ffi_cif, CodePtr},
@@ -7,7 +7,7 @@ use libffi::{
 };
 use mlua::prelude::*;
 
-use super::{FfiData, GetFfiData};
+use super::GetFfiData;
 use crate::ffi::{FfiArg, FfiResult};
 
 pub struct CallableData {
@@ -34,30 +34,38 @@ impl CallableData {
 
     // TODO? async call: if have no lua closure in arguments, fficallble can be called with async way
 
-    pub unsafe fn call(&self, result: &Ref<dyn FfiData>, args: LuaMultiValue) -> LuaResult<()> {
-        result
-            .check_boundary(0, self.result_info.size)
-            .then_some(())
-            .ok_or_else(|| LuaError::external("result boundary check failed"))?;
-
+    pub unsafe fn call(&self, result: LuaValue, args: LuaMultiValue) -> LuaResult<()> {
         // cache Vec => unable to create async call but no allocation
         let mut arg_list = Vec::<*mut c_void>::with_capacity(self.arg_info_list.len());
 
+        let result_pointer = if self.result_info.size == 0 {
+            ptr::null_mut()
+        } else {
+            let result_data = result.get_ffi_data()?;
+            if result_data.check_boundary(0, self.result_info.size) {
+                return Err(LuaError::external("Result boundary check failed"));
+            }
+            result_data.get_pointer()
+        }
+        .cast::<c_void>();
+
         for index in 0..self.arg_info_list.len() {
             let arg_info = self.arg_info_list.get(index).unwrap();
             let arg = args
                 .get(index)
                 .ok_or_else(|| LuaError::external(format!("argument {index} required")))?;
+
             let arg_pointer = if let LuaValue::UserData(userdata) = arg {
+                // BoxData, RefData, ...
                 let data_handle = userdata.get_ffi_data()?;
-                data_handle
-                    .check_boundary(0, arg_info.size)
-                    .then_some(())
-                    .ok_or_else(|| {
-                        LuaError::external(format!("argument {index} boundary check failed"))
-                    })?;
+                if !data_handle.check_boundary(0, arg_info.size) {
+                    return Err(LuaError::external(format!(
+                        "argument {index} boundary check failed"
+                    )));
+                }
                 data_handle.get_pointer()
             } else {
+                // FIXME: buffer, string here
                 return Err(LuaError::external("unimpl"));
             };
             arg_list.push(arg_pointer.cast::<c_void>());
@@ -66,7 +74,7 @@ impl CallableData {
         ffi_call(
             self.cif,
             Some(*self.code.as_safe_fun()),
-            result.get_pointer().cast::<c_void>(),
+            result_pointer,
             arg_list.as_mut_ptr(),
         );
 
@@ -79,14 +87,11 @@ impl LuaUserData for CallableData {
         methods.add_method(
             "call",
             |_lua, this: &CallableData, mut args: LuaMultiValue| {
-                let result_userdata = args.pop_front().ok_or_else(|| {
-                    LuaError::external("first argument must be result data handle")
+                let result = args.pop_front().ok_or_else(|| {
+                    LuaError::external("First argument must be result data handle or nil")
                 })?;
-                let LuaValue::UserData(result) = result_userdata else {
-                    return Err(LuaError::external(""));
-                };
                 // FIXME: clone
-                unsafe { this.call(&result.clone().get_ffi_data()?, args) }
+                unsafe { this.call(result, args) }
             },
         );
         // ref, leak ..?
diff --git a/crates/lune-std-ffi/src/lib.rs b/crates/lune-std-ffi/src/lib.rs
index b008522..917602f 100644
--- a/crates/lune-std-ffi/src/lib.rs
+++ b/crates/lune-std-ffi/src/lib.rs
@@ -1,5 +1,6 @@
 #![allow(clippy::cargo_common_metadata)]
 
+use c::CVoidInfo;
 use data::RefData;
 use lune_utils::TableBuilder;
 use mlua::prelude::*;
@@ -23,6 +24,7 @@ use crate::{
 pub fn module(lua: &Lua) -> LuaResult<LuaTable> {
     let result = TableBuilder::new(lua)?
         .with_values(export_ctypes(lua)?)?
+        .with_value("void", CVoidInfo::new())?
         .with_function("nullRef", |lua, ()| create_nullptr(lua))?
         .with_function("box", |_lua, size: usize| Ok(BoxData::new(size)))?
         .with_function("open", |_lua, name: String| LibData::new(name))?
diff --git a/tests/ffi/external_print/init.luau b/tests/ffi/external_print/init.luau
new file mode 100644
index 0000000..4dad523
--- /dev/null
+++ b/tests/ffi/external_print/init.luau
@@ -0,0 +1,18 @@
+local ffi = require("@lune/ffi")
+
+local testdir = "./tests/ffi/external_print"
+
+local compile = require("../utility/compile")
+compile(`{testdir}/lib.c`, `{testdir}/lib.so`)
+
+local lib = ffi.open(`{testdir}/lib.so`)
+
+local function test_hello_world()
+	local add_int = ffi.fnInfo({}, ffi.void)
+
+	local hello_world_caller = add_int:callable(lib:find("hello_world"))
+
+	hello_world_caller:call(nil)
+end
+
+test_hello_world()
diff --git a/tests/ffi/external_print/lib.c b/tests/ffi/external_print/lib.c
new file mode 100644
index 0000000..d650492
--- /dev/null
+++ b/tests/ffi/external_print/lib.c
@@ -0,0 +1,5 @@
+#include<stdio.h>
+
+void hello_world() {
+    printf("Hello world from external function!");
+}
diff --git a/types/ffi.luau b/types/ffi.luau
index 80927a1..2a7d767 100644
--- a/types/ffi.luau
+++ b/types/ffi.luau
@@ -61,6 +61,10 @@ export type CStructInfo = {
 	writeData: (self: CStructInfo, target: (Ref|Box), table: { any }, offset: number?) -> (),
 }
 
+export type CVoidInfo = {
+	ptrInfo: (self: CVoidInfo) -> CPtrInfo<CVoidInfo>,
+}
+
 type NumCType<T> = CTypeInfo<T, (number|any)>
 
 -- Fixed size Rust-style types --
@@ -126,6 +130,7 @@ export type CTypes =
 	| CPtrInfo<CTypes>
 	| CFnInfo
 	| CStructInfo
+	| CVoidInfo
 
 export type Ref = {
 	deref: (self: Ref) -> Ref,
@@ -147,12 +152,12 @@ export type Lib = {
 }
 
 export type Callable = {
-	call: (self: Callable, result: (Ref | Box), ...(Ref | Box))->();
+	call: (self: Callable, result: (Ref | Box)?, ...(Ref | Box))->();
 }
 
 local ffi = {}
 
-ffi.u8 = (nil :: unknown) :: u8
+ffi.u8 = {} :: u8
 ffi.u16 = {} :: u16
 ffi.u32 = {} :: u32
 ffi.u64 = {} :: u64
@@ -181,6 +186,8 @@ ffi.ulong = {} :: ulong
 ffi.longlong = {} :: longlong
 ffi.ulonglong = {} :: ulonglong
 
+ffi.void = {} :: CVoidInfo
+
 function ffi.nullRef(): Ref
 	return nil :: any
 end