diff --git a/autopush_rs/src/call.rs b/autopush_rs/src/call.rs
index 1a848d7d..73b0f90a 100644
--- a/autopush_rs/src/call.rs
+++ b/autopush_rs/src/call.rs
@@ -163,6 +163,7 @@ enum Call {
         message_month: String,
         messages: Vec<protocol::Notification>,
     },
+
 }
 
 #[derive(Deserialize)]
diff --git a/autopush_rs/src/client.rs b/autopush_rs/src/client.rs
index 3450f300..e1fb3089 100644
--- a/autopush_rs/src/client.rs
+++ b/autopush_rs/src/client.rs
@@ -409,6 +409,11 @@ where
                     ClientMessage::Unregister { channel_id, code } => {
                         self.data.process_unregister(channel_id, code)
                     }
+                    ClientMessage::Nack { .. } => {
+                        self.data.srv.metrics.incr("ua.command.nack").ok();
+                        self.data.webpush.as_mut().unwrap().stats.nacks += 1;
+                        ClientState::WaitingForAcks
+                    }
                     ClientMessage::Ack { updates } => self.data.process_acks(updates),
                     _ => return Err("Invalid state transition".into()),
                 }
@@ -435,6 +440,11 @@ where
                     Either::A(ClientMessage::Unregister { channel_id, code }) => {
                         self.data.process_unregister(channel_id, code)
                     }
+                    Either::A(ClientMessage::Nack { .. }) => {
+                        self.data.srv.metrics.incr("ua.command.nack").ok();
+                        self.data.webpush.as_mut().unwrap().stats.nacks += 1;
+                        ClientState::WaitingForAcks
+                    }
                     Either::B(ServerNotification::Notification(notif)) => {
                         let webpush = self.data.webpush.as_mut().unwrap();
                         webpush.unacked_direct_notifs.push(notif.clone());
diff --git a/autopush_rs/src/protocol.rs b/autopush_rs/src/protocol.rs
index 510758ed..cf634b83 100644
--- a/autopush_rs/src/protocol.rs
+++ b/autopush_rs/src/protocol.rs
@@ -40,6 +40,12 @@ pub enum ClientMessage {
     },
 
     Ack { updates: Vec<ClientAck> },
+
+    Nack {
+        code: Option<i32>,
+        version: String,
+    },
+
 }
 
 #[derive(Deserialize)]