diff --git a/dronecan/driver/slcan.py b/dronecan/driver/slcan.py
index c9231c5..4a52169 100644
--- a/dronecan/driver/slcan.py
+++ b/dronecan/driver/slcan.py
@@ -408,9 +408,9 @@ def __init__(self, conn, rx_queue, tx_queue, termination_condition):
         self._termination_condition = termination_condition
 
     def _send_frame(self, frame):
-        marker = 'D' if frame.canfd else 'T'
+        marker = 'D' if frame.canfd else ('T' if frame.extended else 't')
         dlc_len = CANFrame.datalength_to_dlc(len(frame.data))
-        line = '%s%X%s\r' % (('%c%08X' if frame.extended else 't%03X') % (marker, frame.id),
+        line = '%c%s%X%s\r' % (marker, ('%08X' if frame.extended else '%03X') % (frame.id),
                              dlc_len,
                              binascii.b2a_hex(frame.data).decode('ascii'))