diff --git a/ccid/CCID_Tests.ttcn b/ccid/CCID_Tests.ttcn
index c620b0b..2256025 100644
--- a/ccid/CCID_Tests.ttcn
+++ b/ccid/CCID_Tests.ttcn
@@ -379,7 +379,7 @@
 	f_ccid_power_on();
 	f_ccid_set_par(ts_ProtoDataT0(ISO7816_FI_512_5MHz, ISO7816_DI_32));
 	for (i := 0; i < 1000; i := i+1) {
-		f_ccid_xfr(c_UICC_SELECT_MF, ?);
+		f_ccid_xfr(c_UICC_SELECT_MF, '??'O);
 	}
 }
 testcase TC_select_mf() runs on Test_CT