diff --git a/library/RLCMAC_CSN1_Types.ttcn b/library/RLCMAC_CSN1_Types.ttcn
index d41f9e1..00b6f2d 100644
--- a/library/RLCMAC_CSN1_Types.ttcn
+++ b/library/RLCMAC_CSN1_Types.ttcn
@@ -281,7 +281,7 @@
 		uint7_t		ma_bitmap_length,
 		bitstring	ma_bitmap,
 		BIT1		maio_2_present,
-		BIT6		maio_2
+		BIT6		maio_2 optional
 	} with {
 		variant (ma_bitmap_length) "LENGTHTO (ma_bitmap)"
 		variant (ma_bitmap_length) "UNIT(bits)"