diff --git a/pyVoIP/SIP.py b/pyVoIP/SIP.py
index 5bd9867..41cdb8e 100644
--- a/pyVoIP/SIP.py
+++ b/pyVoIP/SIP.py
@@ -583,10 +583,16 @@ def start(self):
      
   def stop(self):
     self.NSD = False
-    self.registerThread.cancel()
-    self.deregister()
-    self.s.close()
-    self.out.close()
+    if self.registerThread:
+      self.registerThread.cancel()
+      self.deregister()
+    self._close_sockets()
+
+  def _close_sockets(self):
+    if self.s:
+      self.s.close()
+    if self.out:
+      self.out.close()
     
   def genCallID(self):
     return hashlib.sha256(str(self.callID.next()).encode('utf8')).hexdigest()[0:32]+"@"+self.myIP+":"+str(self.myPort)