diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index ed5d994955..99b156ed17 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -6000,7 +6000,8 @@ static int respprep(struct sip_request *resp, struct sip_pvt *p, const char *msg
 	add_header(resp, "To", ot);
 	copy_header(resp, req, "Call-ID");
 	copy_header(resp, req, "CSeq");
-	add_header(resp, "User-Agent", global_useragent);
+	if (!ast_strlen_zero(global_useragent))
+		add_header(resp, "User-Agent", global_useragent);
 	add_header(resp, "Allow", ALLOWED_METHODS);
 	add_header(resp, "Supported", SUPPORTED_EXTENSIONS);
 	if (msg[0] == '2' && (p->method == SIP_SUBSCRIBE || p->method == SIP_REGISTER)) {
@@ -6117,7 +6118,8 @@ static int reqprep(struct sip_request *req, struct sip_pvt *p, int sipmethod, in
 	copy_header(req, orig, "Call-ID");
 	add_header(req, "CSeq", tmp);
 
-	add_header(req, "User-Agent", global_useragent);
+	if (!ast_strlen_zero(global_useragent))
+		add_header(req, "User-Agent", global_useragent);
 
 	if (!ast_strlen_zero(p->rpid))
 		add_header(req, "Remote-Party-ID", p->rpid);
@@ -7269,7 +7271,8 @@ static void initreqprep(struct sip_request *req, struct sip_pvt *p, int sipmetho
 	add_header(req, "Contact", p->our_contact);
 	add_header(req, "Call-ID", p->callid);
 	add_header(req, "CSeq", tmp);
-	add_header(req, "User-Agent", global_useragent);
+	if (!ast_strlen_zero(global_useragent))
+		add_header(req, "User-Agent", global_useragent);
 	if (!ast_strlen_zero(p->rpid))
 		add_header(req, "Remote-Party-ID", p->rpid);
 }
@@ -7863,7 +7866,8 @@ static int transmit_register(struct sip_registry *r, int sipmethod, const char *
 	add_header(&req, "To", to);
 	add_header(&req, "Call-ID", p->callid);
 	add_header(&req, "CSeq", tmp);
-	add_header(&req, "User-Agent", global_useragent);
+	if (!ast_strlen_zero(global_useragent))
+		add_header(&req, "User-Agent", global_useragent);
 
 	
 	if (auth) 	/* Add auth header */