diff --git a/msc/BSC_ConnectionHandler.ttcn b/msc/BSC_ConnectionHandler.ttcn
index 8eb3f7334..01db3d00f 100644
--- a/msc/BSC_ConnectionHandler.ttcn
+++ b/msc/BSC_ConnectionHandler.ttcn
@@ -435,7 +435,7 @@ var GSUP_IE auth_tuple;
 								g_pars.vec.autn,
 								g_pars.vec.res));
 		GSUP.send(ts_GSUP_SAI_RES(g_pars.imsi, auth_tuple));
-		g_pars.vec.kc := f_auth3g_kc();
+		g_pars.vec.kc := f_auth3g_kc(g_pars.vec);
 	} else {
 		g_pars.vec := f_gen_auth_vec_2g();
 		auth_tuple := valueof(ts_GSUP_IE_AuthTuple2G(g_pars.vec.rand,
@@ -548,11 +548,12 @@ function f_expect_common_id() runs on BSC_ConnHdlr
 	}
 }
 
-function f_auth3g_kc() runs on BSC_ConnHdlr return OCT8 {
+/* For UMTS AKA on GERAN, calculate the specific kc from the UMTS AKA ck and ik vectors. */
+function f_auth3g_kc(AuthVector vec) return OCT8 {
 	var integer i;
-	var octetstring res := g_pars.vec.ck[0] xor4b g_pars.vec.ck[0 + 8] xor4b g_pars.vec.ik[0] xor4b g_pars.vec.ik[0 + 8];
+	var octetstring res := vec.ck[0] xor4b vec.ck[0 + 8] xor4b vec.ik[0] xor4b vec.ik[0 + 8];
 	for (i := 1; i < 8; i := i + 1) {
-		var octetstring a := g_pars.vec.ck[i] xor4b g_pars.vec.ck[i + 8] xor4b g_pars.vec.ik[i] xor4b g_pars.vec.ik[i + 8];
+		var octetstring a := vec.ck[i] xor4b vec.ck[i + 8] xor4b vec.ik[i] xor4b vec.ik[i + 8];
 		res := res & a;
 	}