diff --git a/pcu/GPRS_Components.ttcn b/pcu/GPRS_Components.ttcn
index 234d9102c..7093f3146 100644
--- a/pcu/GPRS_Components.ttcn
+++ b/pcu/GPRS_Components.ttcn
@@ -625,12 +625,18 @@ function f_acknackdesc_ack_block(inout AckNackDescription desc, RlcmacDlBlock dl
 		bsn := dl_block.data_egprs.mac_hdr.bsn1;
 	}
 
-	inc := bsn - desc.starting_seq_nr + 1;
 	/* Filling hole? */
 	if (bsn < desc.starting_seq_nr) {
 		desc.receive_block_bitmap[lengthof(desc.receive_block_bitmap) - (desc.starting_seq_nr - bsn)] := int2bit(1, 1);
 		return;
 	}
+	/* Filling hole, wraparound: */
+	if (bsn - desc.starting_seq_nr > lengthof(desc.receive_block_bitmap)) {
+		desc.receive_block_bitmap[lengthof(desc.receive_block_bitmap) - (desc.starting_seq_nr + (218 - bsn))] := int2bit(1, 1);
+		return;
+	}
+
+	inc := bsn - desc.starting_seq_nr + 1;
 
 	/* SSN is increased, and so RBB values need to be moved */
 	for (i := 0; i < lengthof(desc.receive_block_bitmap) - inc; i := i+1) {
@@ -640,7 +646,7 @@ function f_acknackdesc_ack_block(inout AckNackDescription desc, RlcmacDlBlock dl
 		desc.receive_block_bitmap[i] := int2bit(0, 1);
 	}
 	/* Now we can set current bit and update SSN */
-	desc.starting_seq_nr := bsn + 1;
+	desc.starting_seq_nr := (bsn + 1) mod 128;
 	desc.receive_block_bitmap[lengthof(desc.receive_block_bitmap) - 1] := int2bit(1, 1);
 
 	/* Finally update the final_ack bit as requested: */