diff --git a/speech-dispatcher/src/lib.rs b/speech-dispatcher/src/lib.rs
index 38f11a0..1638e73 100644
--- a/speech-dispatcher/src/lib.rs
+++ b/speech-dispatcher/src/lib.rs
@@ -411,17 +411,17 @@ impl Connection {
     }
 
     pub fn set_voice_type(&self, voice_type: VoiceType) -> Result<(), Error> {
-        let v = unsafe { spd_set_voice_type(*self.0, voice_type as u32) };
+        let v = unsafe { spd_set_voice_type(*self.0, voice_type as i32) };
         c_int_to_result(v)
     }
 
     pub fn set_voice_type_all(&self, voice_type: VoiceType) -> Result<(), Error> {
-        let v = unsafe { spd_set_voice_type_all(*self.0, voice_type as u32) };
+        let v = unsafe { spd_set_voice_type_all(*self.0, voice_type as i32) };
         c_int_to_result(v)
     }
 
     pub fn set_voice_type_uid(&self, voice_type: VoiceType, target_uid: u32) -> Result<(), Error> {
-        let v = unsafe { spd_set_voice_type_uid(*self.0, voice_type as u32, target_uid) };
+        let v = unsafe { spd_set_voice_type_uid(*self.0, voice_type as i32, target_uid) };
         c_int_to_result(v)
     }