diff --git a/js/libtextsecure.js b/js/libtextsecure.js
index 0869e4b883..4627482dc2 100644
--- a/js/libtextsecure.js
+++ b/js/libtextsecure.js
@@ -38250,7 +38250,7 @@ MessageReceiver.prototype.extend({
                     destination              : destination,
                     timestamp                : timestamp.toNumber(),
                     message                  : message,
-                    expirationStartTimestamp : expirationStartTimestamp
+                    expirationStartTimestamp : expirationStartTimestamp.toNumber()
                 };
                 this.dispatchEvent(ev);
             }.bind(this));
diff --git a/libtextsecure/message_receiver.js b/libtextsecure/message_receiver.js
index 7878f4908a..85f01e96db 100644
--- a/libtextsecure/message_receiver.js
+++ b/libtextsecure/message_receiver.js
@@ -179,7 +179,7 @@ MessageReceiver.prototype.extend({
                     destination              : destination,
                     timestamp                : timestamp.toNumber(),
                     message                  : message,
-                    expirationStartTimestamp : expirationStartTimestamp
+                    expirationStartTimestamp : expirationStartTimestamp.toNumber()
                 };
                 this.dispatchEvent(ev);
             }.bind(this));