diff --git a/speech-dispatcher/src/lib.rs b/speech-dispatcher/src/lib.rs
index 9050b9c..440abb5 100644
--- a/speech-dispatcher/src/lib.rs
+++ b/speech-dispatcher/src/lib.rs
@@ -5,6 +5,7 @@ use std::{
     ffi::{CStr, CString},
     fmt,
     marker::Send,
+    os::raw::c_char,
     sync::Mutex,
 };
 
@@ -130,7 +131,7 @@ unsafe extern "C" fn cb(msg_id: u64, client_id: u64, state: u32) {
     }
 }
 
-unsafe extern "C" fn cb_im(msg_id: u64, client_id: u64, state: u32, index_mark: *mut i8) {
+unsafe extern "C" fn cb_im(msg_id: u64, client_id: u64, state: u32, index_mark: *mut c_char) {
     let index_mark = CStr::from_ptr(index_mark);
     let index_mark = index_mark.to_string_lossy().to_string();
     let state = match state {
@@ -353,7 +354,7 @@ impl Connection {
     }
 
     pub fn wchar(&self, priority: Priority, wchar: i32) -> bool {
-        let v = unsafe { spd_wchar(self.0, priority as u32, wchar) };
+        let v = unsafe { spd_wchar(self.0, priority as u32, wchar as wchar_t) };
         i32_to_bool(v)
     }