diff --git a/pcu/PCUIF_Components.ttcn b/pcu/PCUIF_Components.ttcn
index be7aaeb..66b2e21 100644
--- a/pcu/PCUIF_Components.ttcn
+++ b/pcu/PCUIF_Components.ttcn
@@ -374,6 +374,11 @@
 	}
 }
 
+private function fn2macblock(uint32_t fn)  return uint8_t
+{
+	return (fn mod 52) / 4;
+}
+
 /* Get first message from queue. true if non-empty, false otherwise */
 private function f_tx_data_ind_fn(integer bts_nr, integer fn)
 runs on RAW_PCU_BTS_CT
@@ -399,7 +404,7 @@
 				f_PCUIF_MsgQueue_dequeue(pdtch_data_queue, pcu_msg);
 				/* Patch TDMA frame / block number */
 				pcu_msg.u.data_ind.fn := fn;
-				pcu_msg.u.data_ind.block_nr := 0; /* FIXME! */
+				pcu_msg.u.data_ind.block_nr := fn2macblock(fn);
 				//log(prefix, "DATA.ind");
 			} else if (has_msg and pcu_msg.u.data_ind.fn < fn) {
 					setverdict(fail, "We are late scheduling the block! ", pcu_msg.u.data_ind.fn, " < ", fn);
@@ -439,7 +444,7 @@
 
 			/* Patch TDMA frame / block number and send */
 			pcu_msg.u.rts_req.fn := event.data.tdma_fn;
-			pcu_msg.u.rts_req.block_nr := 0; /* FIXME! */
+			pcu_msg.u.rts_req.block_nr := fn2macblock(event.data.tdma_fn);
 			PCUIF.send(pcu_msg);
 		}
 
@@ -462,7 +467,7 @@
 
 		/* Patch TDMA frame / block number and send */
 		pcu_msg.u.rts_req.fn := ev_begin_fn;
-		pcu_msg.u.rts_req.block_nr := 0; /* FIXME! */
+		pcu_msg.u.rts_req.block_nr := fn2macblock(ev_begin_fn);
 		PCUIF.send(pcu_msg);
 		repeat;
 		}