diff --git a/library/Osmocom_Types.ttcn b/library/Osmocom_Types.ttcn
index d034a74..6653408 100644
--- a/library/Osmocom_Types.ttcn
+++ b/library/Osmocom_Types.ttcn
@@ -179,6 +179,15 @@
 	}
 }
 
+function char2oct_tmpl_present(template (present) charstring inp) return template (present) octetstring
+{
+	if (istemplatekind(inp, "?")) {
+		return ?;
+	} else {
+		return char2oct(valueof(inp));
+	}
+}
+
 function hex2str_tmpl(template hexstring inp) return template charstring
 {
 	if (istemplatekind(inp, "omit")) {