diff --git a/library/GSM_Types.ttcn b/library/GSM_Types.ttcn
index e1d6b48..e57575d 100644
--- a/library/GSM_Types.ttcn
+++ b/library/GSM_Types.ttcn
@@ -160,4 +160,12 @@
 		sapi := sapi
 	};
 
+	function f_hex_is_odd_length(hexstring digits) return bitstring {
+		if (lengthof(digits) rem 2 == 1) {
+			return '1'B;
+		} else {
+			return '0'B;
+		}
+	}
+
 } with { encode "RAW"; variant "FIELDORDER(msb)" }