diff --git a/library/Osmocom_Types.ttcn b/library/Osmocom_Types.ttcn
index 2e71123..e7c9776 100644
--- a/library/Osmocom_Types.ttcn
+++ b/library/Osmocom_Types.ttcn
@@ -178,5 +178,31 @@ function f_pad_bcd_number(hexstring number) return hexstring {
        }
 }

+/* Presence bits are heavily used in CSN.1: { 0 | 1 < field > } */
+function f_pres_bit(template (omit) anytype field) return BIT1
+{
+       if (not istemplatekind(field, "omit")) {
+               return '1'B;
+       } else {
+               return '0'B;
+       }
+}
+
+/* Unfortunately, this trick does not work:
+ * TITAN error: Reference to non-existent field `OCT1' in union template for type `@Osmocom_Types.anytype'
+ * TITAN note: @Osmocom_Types.anytype has no fields */
+testcase TC_f_pres_bit() runs on CT_TUWAT {
+       var template (omit) OCT1 field;
+       var BIT1 field_ind;
+
+       field := '2B'O;
+       field_ind := f_pres_bit({ OCT1 := field });
+       log("Test #1: field=", field, " field_ind=", field_ind);
+
+       field := omit;
+       field_ind := f_pres_bit({ OCT1 := field });
+       log("Test #2: field=", field, " field_ind=", field_ind);
+}
+

 } with { encode "RAW"; variant "FIELDORDER(msb)" }