diff --git a/src/common/connection.py b/src/common/connection.py
index e5ce35fd4..5ebd69064 100644
--- a/src/common/connection.py
+++ b/src/common/connection.py
@@ -1174,7 +1174,7 @@ class Connection(CommonConnection, ConnectionHandlers):
                     None, conn=self, con=con, port=port,
                     secure_tuple=secure_tuple))
                 return
-            self.on_client_cert_passphrase(None, con, port, secure_tuple)
+            self.on_client_cert_passphrase('', con, port, secure_tuple)
 
         else:
             self._connect_to_next_host(retry)