diff --git a/core/plug-in/sipctrl/SipCtrlInterface.cpp b/core/plug-in/sipctrl/SipCtrlInterface.cpp
index 9763c38f..63f5de1f 100644
--- a/core/plug-in/sipctrl/SipCtrlInterface.cpp
+++ b/core/plug-in/sipctrl/SipCtrlInterface.cpp
@@ -199,8 +199,9 @@ int SipCtrlInterface::send(const AmSipRequest &req, string &serKey)
  	}
     }
 
-    msg->hdrs.push_back(new sip_header(0,"User-Agent",
-				       stl2cstr(AmConfig::Signature)));
+    if (AmConfig::Signature.length())
+      msg->hdrs.push_back(new sip_header(0,"User-Agent",
+					 stl2cstr(AmConfig::Signature)));
 
     if(!req.hdrs.empty()) {