--- serial/serialposix.py
+++ serial/serialposix.py
@@ -215,7 +215,7 @@
     # no exception, just continue with a brave attempt to build a device name
     # even if the device name is not correct for the platform it has chances
     # to work using a string with the real device name as port parameter.
-    def device(portum):
+    def device(portnum):
         return '/dev/ttyS%d' % portnum
     def set_special_baudrate(port, baudrate):
         raise SerialException("sorry don't know how to handle non standard baud rate on this platform")