diff --git a/library/GSM_Types.ttcn b/library/GSM_Types.ttcn
index c7b7991..0289b08 100644
--- a/library/GSM_Types.ttcn
+++ b/library/GSM_Types.ttcn
@@ -26,6 +26,19 @@
 		CS1, CS2, CS3, CS4
 	};
 
+	function f_gprs_blocksize(GprsCodingScheme cs) return integer {
+		select (cs) {
+		case (CS1) { return 22 }
+		case (CS2) { return 32 }
+		case (CS3) { return 38 }
+		case (CS3) { return 52 }
+		case else {
+			setverdict(fail, "Invalid GPRS CS ", cs);
+			return -1;
+			}
+		}
+	}
+
 	/* 10.5.2.8 */
 	type enumerated ChannelNeeded {
 		CHAN_NEED_ANY	(0),