1 files changed, 3 insertions, 0 deletions
diff --git a/addons/mail/static/src/models/thread/thread.js b/addons/mail/static/src/models/thread/thread.js
index 31339e063f3..4739e59f91e 100644
--- a/addons/mail/static/src/models/thread/thread.js
+++ b/addons/mail/static/src/models/thread/thread.js
@@ -1344,6 +1344,9 @@ function factory(dependencies) {
             const index = this.orderedMessages.findIndex(message =>
                 message.id === this.lastSeenByCurrentPartnerMessageId
             );
+            if (index === -1) {
+                return [['unlink']];
+            }
             const message = this.orderedMessages[index + 1];
             if (!message) {
                 return [['unlink']];