diff --git a/library/GSM_RR_Types.ttcn b/library/GSM_RR_Types.ttcn
index 76b03a919..2ad3b6adc 100644
--- a/library/GSM_RR_Types.ttcn
+++ b/library/GSM_RR_Types.ttcn
@@ -296,7 +296,7 @@ module GSM_RR_Types {
 	/* 10.5.2.21 */
 	type record MobileAllocationLV {
 		uint8_t 	len,
-		bitstring	ma
+		bitstring	ma length (0..64)
 	} with {
 		variant (len) "LENGTHTO(ma)"
 		variant (ma) "BYTEORDER(first), BITORDER(msb)"