diff --git a/src/main.rs b/src/main.rs
index 44058b2..df7d6df 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -958,23 +958,50 @@ async fn compute_read_markers(
         if user == own_user {
             continue;
         }
-        let receipt_eid = match room
+        let (receipt_eid, receipt_ts) = match room
             .load_user_receipt(ReceiptType::Read, ReceiptThread::Unthreaded, user)
             .await
         {
-            Ok(Some((eid, _))) => eid,
+            Ok(Some((eid, r))) => {
+                let ts = r.ts.map(|t| ts_secs_from(t.0)).unwrap_or(0);
+                (eid, ts)
+            }
             _ => continue,
         };
-        let Some(&user_pos) = positions.get(&receipt_eid) else {
-            continue;
+
+        // Three cases:
+        //   1. Receipt event is in our window → mark messages at idx <= user_pos
+        //   2. Receipt is for an event newer than our window (timestamp-based)
+        //      → mark every message as read
+        //   3. Receipt is older than our window → mark nothing
+        let user_msg_idx_inclusive: Option<usize> = if let Some(&p) = positions.get(&receipt_eid) {
+            Some(p)
+        } else {
+            // Compare receipt ts with the newest message ts
+            let newest_msg_ts = timeline
+                .iter()
+                .rev()
+                .find_map(|t| match t {
+                    TimelineItem::Message { ts, .. } => Some(*ts),
+                    _ => None,
+                })
+                .unwrap_or(0);
+            if receipt_ts > 0 && receipt_ts >= newest_msg_ts {
+                // User has read past our entire window
+                Some(timeline.len().saturating_sub(1))
+            } else {
+                None
+            }
         };
-        // Mark this user as a reader for all messages at index <= user_pos
-        for item in timeline.iter().take(user_pos + 1) {
-            if let TimelineItem::Message { event_id, .. } = item {
-                readers
-                    .entry(event_id.clone())
-                    .or_default()
-                    .push(user.clone());
+
+        if let Some(up_to) = user_msg_idx_inclusive {
+            for item in timeline.iter().take(up_to + 1) {
+                if let TimelineItem::Message { event_id, .. } = item {
+                    readers
+                        .entry(event_id.clone())
+                        .or_default()
+                        .push(user.clone());
+                }
             }
         }
     }