diff --git a/src/receive_imf.rs b/src/receive_imf.rs
index 76c9934ae..3f2588233 100644
--- a/src/receive_imf.rs
+++ b/src/receive_imf.rs
@@ -2093,13 +2093,14 @@ async fn create_group(
             }
             members.extend(to_ids);
 
-            chat::add_to_chat_contacts_table(
-                context,
-                mime_parser.timestamp_sent,
-                new_chat_id,
-                &members,
-            )
-            .await?;
+            // Add all members with 0 timestamp
+            // because we don't know the real timestamp of their addition.
+            // This will allow other senders who support
+            // `Chat-Group-Member-Timestamps` to overwrite
+            // timestamps later.
+            let timestamp = 0;
+
+            chat::add_to_chat_contacts_table(context, timestamp, new_chat_id, &members).await?;
         }
 
         context.emit_event(EventType::ChatModified(new_chat_id));
diff --git a/src/receive_imf/receive_imf_tests.rs b/src/receive_imf/receive_imf_tests.rs
index 588a74e4b..f2798e9e9 100644
--- a/src/receive_imf/receive_imf_tests.rs
+++ b/src/receive_imf/receive_imf_tests.rs
@@ -5485,3 +5485,69 @@ async fn test_prefer_chat_group_id_over_references() -> Result<()> {
     assert_ne!(chat1.id, chat2.id);
     Ok(())
 }
+
+/// Tests that if member timestamps are unknown
+/// because of the missing `Chat-Group-Member-Timestamps` header,
+/// then timestamps default to zero.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_default_member_timestamps_to_zero() -> Result<()> {
+    let bob = &TestContext::new_bob().await;
+
+    let now = time();
+
+    let date = chrono::DateTime::<chrono::Utc>::from_timestamp(now - 1000, 0)
+        .unwrap()
+        .to_rfc2822();
+    let msg = receive_imf(
+        bob,
+        format!(
+            "Subject: Some group\r\n\
+             From: <alice@example.org>\r\n\
+             To: <bob@example.net>, <claire@example.org>, <fiona@example.org>\r\n\
+             Date: {date}\r\n\
+             Message-ID: <first@localhost>\r\n\
+             Chat-Group-ID: foobarbaz12\n\
+             Chat-Group-Name: foo\n\
+             Chat-Version: 1.0\r\n\
+             \r\n\
+             Hi!\r\n"
+        )
+        .as_bytes(),
+        false,
+    )
+    .await?
+    .unwrap();
+    let chat = Chat::load_from_db(bob, msg.chat_id).await?;
+    assert_eq!(chat.typ, Chattype::Group);
+    assert_eq!(chat::get_chat_contacts(bob, chat.id).await?.len(), 4);
+
+    let date = chrono::DateTime::<chrono::Utc>::from_timestamp(now, 0)
+        .unwrap()
+        .to_rfc2822();
+    receive_imf(
+        bob,
+        format!(
+            "Subject: Some group\r\n\
+             From: <claire@example.org>\r\n\
+             To: <alice@example.org>, <bob@example.net>\r\n\
+             Chat-Group-Past-Members: <fiona@example.org>\r\n\
+             Chat-Group-Member-Timestamps: 1737783000 1737783100 1737783200\r\n\
+             Chat-Group-ID: foobarbaz12\n\
+             Chat-Group-Name: foo\n\
+             Chat-Version: 1.0\r\n\
+             Date: {date}\r\n\
+             Message-ID: <second@localhost>\r\n\
+             \r\n\
+            Hi back!\r\n"
+        )
+        .as_bytes(),
+        false,
+    )
+    .await?
+    .unwrap();
+
+    let chat = Chat::load_from_db(bob, msg.chat_id).await?;
+    assert_eq!(chat.typ, Chattype::Group);
+    assert_eq!(chat::get_chat_contacts(bob, chat.id).await?.len(), 3);
+    Ok(())
+}