--- a/pm_linux/pmlinuxalsa.c
+++ b/pm_linux/pmlinuxalsa.c
@@ -645,7 +645,7 @@ static void handle_event(snd_seq_event_t
     case SND_SEQ_EVENT_SYSEX: {
         const BYTE *ptr = (const BYTE *) ev->data.ext.ptr;
         /* assume there is one sysex byte to process */
-        pm_read_bytes(midi, ptr, ev->data.ext.len, timestamp);
+        pm_read_bytes(midi, (unsigned char*)ptr, ev->data.ext.len, timestamp);
         break;
     }
     case SND_SEQ_EVENT_PORT_UNSUBSCRIBED: {