diff --git a/pyVoIP/SIP.py b/pyVoIP/SIP.py
index 633d695..1cd2d70 100644
--- a/pyVoIP/SIP.py
+++ b/pyVoIP/SIP.py
@@ -1562,7 +1562,7 @@ def gen_ack(self, request: SIPMessage) -> str:
         ackMessage += "Max-Forwards: 70\r\n"
         ackMessage += (
             f"To: {request.headers['To']['raw']};tag="
-            + f"{self.gen_tag()}\r\n"
+            + f"{request.headers['To']['tag']}\r\n"
         )
         ackMessage += f"From: {request.headers['From']['raw']};tag={tag}\r\n"
         ackMessage += f"Call-ID: {request.headers['Call-ID']}\r\n"