diff --git a/io/hpmud/musb.c b/io/hpmud/musb.c

index 755493e..6d9c7fc 100644

--- a/io/hpmud/musb.c

+++ b/io/hpmud/musb.c

@@ -1454,7 +1454,7 @@ enum HPMUD_RESULT __attribute__ ((visibility ("hidden"))) musb_raw_channel_write

                     BUG("unable to write data %s: %d second io timeout\n", msp->device[pc->dindex].uri, sec_timeout);

             }

             else

-                BUG("unable to write data (len = %d) %s: %m\n", msp->device[pc->dindex].uri, len);

+                BUG("unable to write data (len = %d) %s: %m\n", len, msp->device[pc->dindex].uri);

             goto bugout;

         }

 		if(len == 0 && size > 0)