diff --git a/src/chat.rs b/src/chat.rs
index 374c7eb3a..464fb2024 100644
--- a/src/chat.rs
+++ b/src/chat.rs
@@ -3335,7 +3335,7 @@ pub(crate) async fn shall_attach_selfavatar(context: &Context, chat_id: ChatId)
 }
 
 /// Chat mute duration.
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub enum MuteDuration {
     /// Chat is not muted.
     NotMuted,
@@ -3385,6 +3385,7 @@ impl rusqlite::types::FromSql for MuteDuration {
 /// Mutes the chat for a given duration or unmutes it.
 pub async fn set_muted(context: &Context, chat_id: ChatId, duration: MuteDuration) -> Result<()> {
     ensure!(!chat_id.is_special(), "Invalid chat ID");
+    let (context, nosync) = &context.unwrap_nosync();
     context
         .sql
         .execute(
@@ -3394,6 +3395,11 @@ pub async fn set_muted(context: &Context, chat_id: ChatId, duration: MuteDuratio
         .await
         .context(format!("Failed to set mute duration for {chat_id}"))?;
     context.emit_event(EventType::ChatModified(chat_id));
+    if !nosync {
+        let chat = Chat::load_from_db(context, chat_id).await?;
+        chat.add_sync_item(context, ChatAction::SetMuted(duration))
+            .await?;
+    }
     Ok(())
 }
 
@@ -4048,6 +4054,7 @@ impl Context {
             ChatAction::Unblock => chat_id.unblock(self).await,
             ChatAction::Accept => chat_id.accept(self).await,
             ChatAction::SetVisibility(v) => chat_id.set_visibility(self, *v).await,
+            ChatAction::SetMuted(duration) => set_muted(self, chat_id, *duration).await,
         }
         .ok();
         Ok(())
diff --git a/src/sync.rs b/src/sync.rs
index c3c75459e..87fc6d4ab 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -47,6 +47,7 @@ pub(crate) enum ChatAction {
 
     Accept,
     SetVisibility(ChatVisibility),
+    SetMuted(chat::MuteDuration),
 }
 
 #[derive(Debug, Serialize, Deserialize)]
@@ -288,6 +289,8 @@ impl Context {
 
 #[cfg(test)]
 mod tests {
+    use std::time::{Duration, SystemTime};
+
     use anyhow::bail;
     use strum::IntoEnumIterator;
 
@@ -316,13 +319,15 @@ mod tests {
 
         assert!(t.build_sync_json().await?.is_none());
 
-        // Having one test on `SyncData::AlterChat` is sufficient here as `AlterChatData` introduces
-        // enums inside items. Let's avoid in-depth testing of the serialiser here which is an
-        // external crate.
+        // Having one test on `SyncData::AlterChat` is sufficient here as `AlterChatData` with
+        // `ChatAction::SetMuted` introduces enums inside items and SystemTime. Let's avoid in-depth
+        // testing of the serialiser here which is an external crate.
         t.add_sync_item_with_timestamp(
             SyncData::AlterChat(AlterChatData {
                 id: ChatId::ContactAddr("bob@example.net".to_string()),
-                action: ChatAction::Block,
+                action: ChatAction::SetMuted(chat::MuteDuration::Until(
+                    SystemTime::UNIX_EPOCH + Duration::from_millis(42999),
+                )),
             }),
             1631781315,
         )
@@ -351,7 +356,7 @@ mod tests {
         assert_eq!(
             serialized,
             r#"{"items":[
-{"timestamp":1631781315,"data":{"AlterChat":{"id":{"ContactAddr":"bob@example.net"},"action":"Block"}}},
+{"timestamp":1631781315,"data":{"AlterChat":{"id":{"ContactAddr":"bob@example.net"},"action":{"SetMuted":{"Until":{"secs_since_epoch":42,"nanos_since_epoch":999000000}}}}}},
 {"timestamp":1631781316,"data":{"AddQrToken":{"invitenumber":"testinvite","auth":"testauth","grpid":"group123"}}},
 {"timestamp":1631781317,"data":{"DeleteQrToken":{"invitenumber":"123!?\":.;{}","auth":"456","grpid":null}}}
 ]}"#
@@ -425,16 +430,21 @@ mod tests {
             )
             .is_err()); // Unknown enum value
 
-        // Test enums inside items
+        // Test enums inside items and SystemTime
         let sync_items = t.parse_sync_items(
-          r#"{"items":[{"timestamp":1631781318,"data":{"AlterChat":{"id":{"ContactAddr":"bob@example.net"},"action":"Block"}}}]}"#.to_string(),
+            r#"{"items":[{"timestamp":1631781318,"data":{"AlterChat":{"id":{"ContactAddr":"bob@example.net"},"action":{"SetMuted":{"Until":{"secs_since_epoch":42,"nanos_since_epoch":999000000}}}}}}]}"#.to_string(),
         )?;
         assert_eq!(sync_items.items.len(), 1);
         let AlterChat(AlterChatData { id, action }) = &sync_items.items.get(0).unwrap().data else {
             bail!("bad item");
         };
         assert_eq!(*id, ChatId::ContactAddr("bob@example.net".to_string()));
-        assert_eq!(*action, ChatAction::Block);
+        assert_eq!(
+            *action,
+            ChatAction::SetMuted(chat::MuteDuration::Until(
+                SystemTime::UNIX_EPOCH + Duration::from_millis(42999)
+            ))
+        );
 
         // empty item list is okay
         assert_eq!(
@@ -607,6 +617,31 @@ mod tests {
             assert_eq!(alices[1].get_chat(&bob).await.get_visibility(), v);
         }
 
+        use chat::MuteDuration;
+        assert_eq!(
+            alices[1].get_chat(&bob).await.mute_duration,
+            MuteDuration::NotMuted
+        );
+        let mute_durations = [
+            MuteDuration::Forever,
+            MuteDuration::Until(SystemTime::now() + Duration::from_secs(42)),
+            MuteDuration::NotMuted,
+        ];
+        for m in mute_durations {
+            chat::set_muted(&alices[0], a0b_chat_id, m).await?;
+            sync(&alices).await?;
+            let m = match m {
+                MuteDuration::Until(time) => MuteDuration::Until(
+                    SystemTime::UNIX_EPOCH
+                        + Duration::from_secs(
+                            time.duration_since(SystemTime::UNIX_EPOCH)?.as_secs(),
+                        ),
+                ),
+                _ => m,
+            };
+            assert_eq!(alices[1].get_chat(&bob).await.mute_duration, m);
+        }
+
         Ok(())
     }
 }