diff --git a/src/chat.rs b/src/chat.rs
index 464fb2024..685bc8070 100644
--- a/src/chat.rs
+++ b/src/chat.rs
@@ -372,7 +372,7 @@ impl ChatId {
                             context,
                             "Blocking the contact {contact_id} to block 1:1 chat."
                         );
-                        Contact::block(context, contact_id).await?;
+                        Contact::block(&context.nosync(), contact_id).await?;
                     }
                 }
             }
@@ -388,6 +388,7 @@ impl ChatId {
         }
 
         if !nosync {
+            // NB: For a 1:1 chat this currently triggers `Contact::block()` on other devices.
             chat.add_sync_item(context, ChatAction::Block).await?;
         }
         Ok(())
@@ -401,6 +402,9 @@ impl ChatId {
 
         if !nosync {
             let chat = Chat::load_from_db(context, self).await?;
+            // TODO: For a 1:1 chat this currently triggers `Contact::unblock()` on other devices.
+            // Maybe we should unblock the contact locally too, this would also resolve discrepancy
+            // with `block()` which also blocks the contact.
             chat.add_sync_item(context, ChatAction::Unblock).await?;
         }
         Ok(())
@@ -4035,6 +4039,11 @@ impl Context {
                     warn!(self, "sync_alter_chat: No contact for addr '{addr}'.");
                     return Ok(());
                 };
+                match &data.action {
+                    ChatAction::Block => return Contact::block(self, contact_id).await,
+                    ChatAction::Unblock => return Contact::unblock(self, contact_id).await,
+                    _ => (),
+                }
                 let Some(chat_id) = ChatId::lookup_by_contact(self, contact_id).await? else {
                     warn!(self, "sync_alter_chat: No chat for addr '{addr}'.");
                     return Ok(());
diff --git a/src/contact.rs b/src/contact.rs
index 2874e94cd..8068cb654 100644
--- a/src/contact.rs
+++ b/src/contact.rs
@@ -32,6 +32,7 @@ use crate::mimeparser::AvatarAction;
 use crate::param::{Param, Params};
 use crate::peerstate::{Peerstate, PeerstateVerifiedStatus};
 use crate::sql::{self, params_iter};
+use crate::sync::{self, SyncData};
 use crate::tools::{
     duration_to_str, get_abs_path, improve_single_line_input, strip_rtlo_characters, time,
     EmailAddress,
@@ -494,7 +495,7 @@ impl Contact {
             }
         }
         if blocked {
-            Contact::unblock(context, contact_id).await?;
+            Contact::unblock(&context.nosync(), contact_id).await?;
         }
 
         Ok(contact_id)
@@ -1393,6 +1394,7 @@ async fn set_block_contact(
         "Can't block special contact {}",
         contact_id
     );
+    let (context, nosync) = &context.unwrap_nosync();
 
     let contact = Contact::get_by_id(context, contact_id).await?;
 
@@ -1438,6 +1440,19 @@ WHERE type=? AND id IN (
                 chat_id.unblock(&context.nosync()).await?;
             }
         }
+
+        if !nosync {
+            let action = match new_blocking {
+                true => sync::ChatAction::Block,
+                false => sync::ChatAction::Unblock,
+            };
+            context
+                .add_sync_item(SyncData::AlterChat(sync::AlterChatData {
+                    id: sync::ChatId::ContactAddr(contact.addr.clone()),
+                    action,
+                }))
+                .await?;
+        }
     }
 
     Ok(())
diff --git a/src/sync.rs b/src/sync.rs
index 87fc6d4ab..beef9b7cd 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -36,15 +36,7 @@ pub(crate) enum ChatId {
 #[derive(Debug, Serialize, Deserialize, PartialEq)]
 pub(crate) enum ChatAction {
     Block,
-    // TODO: Actually unblocking a chat is not a public API. `Contact::unblock()` is what a user
-    // does actually, but it doesn't call `chat::ChatId::unblock()`. So, unblocking chats sync
-    // doesn't work now, but let it be implemented on chats nevertheless. The straightforward fix is
-    // to call `chat::ChatId::unblock()` in a context of user action.
-    //
-    // But it still works if a message is sent to a blocked contact because
-    // `chat::ChatId::unblock()` is called then.
     Unblock,
-
     Accept,
     SetVisibility(ChatVisibility),
     SetMuted(chat::MuteDuration),
@@ -604,6 +596,18 @@ mod tests {
         sync(&alices).await?;
         assert_eq!(alices[1].get_chat(&bob).await.blocked, Blocked::Not);
 
+        // Unblocking a 1:1 chat doesn't unblock the contact currently.
+        let a0b_contact_id = alices[0].add_or_lookup_contact(&bob).await.id;
+        Contact::unblock(&alices[0], a0b_contact_id).await?;
+
+        assert!(!alices[1].add_or_lookup_contact(&bob).await.is_blocked());
+        Contact::block(&alices[0], a0b_contact_id).await?;
+        sync(&alices).await?;
+        assert!(alices[1].add_or_lookup_contact(&bob).await.is_blocked());
+        Contact::unblock(&alices[0], a0b_contact_id).await?;
+        sync(&alices).await?;
+        assert!(!alices[1].add_or_lookup_contact(&bob).await.is_blocked());
+
         assert_eq!(
             alices[1].get_chat(&bob).await.get_visibility(),
             ChatVisibility::Normal