diff --git a/src/backends/appkit.rs b/src/backends/appkit.rs
index 8584188..4b9a089 100644
--- a/src/backends/appkit.rs
+++ b/src/backends/appkit.rs
@@ -7,7 +7,7 @@ use objc::declare::ClassDecl;
 use objc::runtime::*;
 use objc::*;
 
-use crate::{Backend, Error, Features};
+use crate::{Backend, Error, Features, UtteranceId};
 
 pub struct AppKit(*mut Object, *mut Object);
 
@@ -101,7 +101,7 @@ impl Backend for AppKit {
         }
     }
 
-    fn speak(&mut self, text: &str, interrupt: bool) -> Result<(), Error> {
+    fn speak(&mut self, text: &str, interrupt: bool) -> Result<Option<UtteranceId>, Error> {
         trace!("speak({}, {})", text, interrupt);
         if interrupt {
             self.stop()?;
@@ -110,7 +110,7 @@ impl Backend for AppKit {
             let str = NSString::alloc(nil).init_str(text);
             let _: () = msg_send![self.1, enqueueAndSpeak: str];
         }
-        Ok(())
+        Ok(None)
     }
 
     fn stop(&mut self) -> Result<(), Error> {
diff --git a/src/backends/av_foundation.rs b/src/backends/av_foundation.rs
index a04eaea..fdd9cd7 100644
--- a/src/backends/av_foundation.rs
+++ b/src/backends/av_foundation.rs
@@ -1,12 +1,14 @@
 #[cfg(any(target_os = "macos", target_os = "ios"))]
 #[link(name = "AVFoundation", kind = "framework")]
+use std::sync::Mutex;
+
 use cocoa_foundation::base::{id, nil};
 use cocoa_foundation::foundation::NSString;
 use log::{info, trace};
 use objc::runtime::*;
 use objc::*;
 
-use crate::{Backend, Error, Features};
+use crate::{Backend, Error, Features, UtteranceId};
 
 pub struct AvFoundation {
     synth: *mut Object,
@@ -41,21 +43,22 @@ impl Backend for AvFoundation {
         }
     }
 
-    fn speak(&mut self, text: &str, interrupt: bool) -> Result<(), Error> {
+    fn speak(&mut self, text: &str, interrupt: bool) -> Result<Option<UtteranceId>, Error> {
         trace!("speak({}, {})", text, interrupt);
         if interrupt {
             self.stop()?;
         }
+        let utterance: id;
         unsafe {
             let str = NSString::alloc(nil).init_str(text);
-            let utterance: id = msg_send![class!(AVSpeechUtterance), alloc];
+            utterance = msg_send![class!(AVSpeechUtterance), alloc];
             let _: () = msg_send![utterance, initWithString: str];
             let _: () = msg_send![utterance, setRate: self.rate];
             let _: () = msg_send![utterance, setVolume: self.volume];
             let _: () = msg_send![utterance, setPitchMultiplier: self.pitch];
             let _: () = msg_send![self.synth, speakUtterance: utterance];
         }
-        Ok(())
+        Ok(Some(UtteranceId::AvFoundation(utterance)))
     }
 
     fn stop(&mut self) -> Result<(), Error> {
diff --git a/src/lib.rs b/src/lib.rs
index 2d494cf..c8166a2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -48,6 +48,8 @@ pub enum UtteranceId {
     Web(u64),
     #[cfg(windows)]
     WinRT(u64),
+    #[cfg(any(target_os = "macos", target_os = "ios"))]
+    AvFoundation(id),
 }
 
 pub struct Features {