diff --git a/pySim/transport/calypso.py b/pySim/transport/calypso.py
index 467d5ee..3c223e6 100644
--- a/pySim/transport/calypso.py
+++ b/pySim/transport/calypso.py
@@ -115,7 +115,7 @@
 	def wait_for_card(self, timeout = None, newcardonly = False):
 		pass # Nothing to do really ...
 
-	def send_apdu_raw(self, pdu):
+	def _send_apdu_raw(self, pdu):
 
 		# Request FULL reset
 		req_msg = L1CTLMessageSIM(h2b(pdu))