diff --git a/lib/session/call-session.js b/lib/session/call-session.js
index 154a09ab..d378c932 100644
--- a/lib/session/call-session.js
+++ b/lib/session/call-session.js
@@ -475,7 +475,7 @@ class CallSession extends Emitter {
   _evalUnansweredCallPrecondition(task, callSid) {
     if (!this.req) throw new Error('invalid precondition unanswered_call for outbound call');
     if (this.callGone) new Error(`${BADPRECONDITIONS}: call gone`);
-    if (this.req.finalResponseSent) {
+    if (this.res.finalResponseSent) {
       throw new Error(`${BADPRECONDITIONS}: final sip status already sent`);
     }
     return {req: this.req, res: this.res};