diff --git a/sys/transceiver/transceiver.c b/sys/transceiver/transceiver.c
index cef4a23287..4374d67d57 100644
--- a/sys/transceiver/transceiver.c
+++ b/sys/transceiver/transceiver.c
@@ -211,6 +211,7 @@ uint8_t transceiver_register(transceiver_type_t t, int pid)
 {
     uint8_t i;
 
+    /* find pid in registered threads or first unused space */
     for (i = 0; ((reg[i].pid != pid) &&
                 (i < TRANSCEIVER_MAX_REGISTERED) &&
                 (reg[i].transceivers != TRANSCEIVER_NONE)); i++);