diff --git a/frappe/public/js/frappe/form/footer/form_timeline.js b/frappe/public/js/frappe/form/footer/form_timeline.js
index 57acf85f7c..2d27fe12c3 100644
--- a/frappe/public/js/frappe/form/footer/form_timeline.js
+++ b/frappe/public/js/frappe/form/footer/form_timeline.js
@@ -575,8 +575,8 @@ class FormTimeline extends BaseTimeline {
 			}
 			if (reply_all) {
 				// if reply_all then add cc and bcc as well.
-				args.cc += communication_doc.cc;
-				args.bcc = communication_doc.bcc;
+				args.cc += cstr(communication_doc.cc);
+				args.bcc = cstr(communication_doc.bcc);
 			}
 		}