diff --git a/lib/call-session.js b/lib/call-session.js
index 257e8af..4f08e3a 100644
--- a/lib/call-session.js
+++ b/lib/call-session.js
@@ -13,8 +13,8 @@ const MS_TEAMS_SIP_ENDPOINT = 'sip.pstnhub.microsoft.com';
 const createBLegFromHeader = (req) => {
   const from = req.getParsedHeader('From');
   const uri = parseUri(from.uri);
-  if (uri && uri.user) return `sip:${uri.user}@localhost`;
-  return 'sip:anonymous@localhost';
+  if (uri && uri.user) return `<sip:${uri.user}@localhost>`;
+  return '<sip:anonymous@localhost>';
 };
 
 class CallSession extends Emitter {