diff --git a/openbsc/include/openbsc/bsc_msg_filter.h b/openbsc/include/openbsc/bsc_msg_filter.h
index a974195c..64890500 100644
--- a/openbsc/include/openbsc/bsc_msg_filter.h
+++ b/openbsc/include/openbsc/bsc_msg_filter.h
@@ -11,9 +11,7 @@ struct vty;
 struct gsm48_hdr;
 
 /* TODO: remove */
-struct bsc_nat_parsed;
 struct bsc_connection;
-struct nat_sccp_connection;
 
 struct bsc_filter_reject_cause {
 	int lu_reject_cause;
@@ -58,6 +56,11 @@ struct bsc_msg_acc_lst_entry {
 	int lu_reject_cause;
 };
 
+struct bsc_filter_state {
+	char *imsi;
+	int imsi_checked;
+};
+
 
 int bsc_filter_barr_adapt(void *ctx, struct rb_root *rbtree, const struct osmo_config_list *);
 int bsc_filter_barr_find(struct rb_root *root, const char *imsi, int *cm, int *lu);
@@ -71,7 +74,7 @@ int bsc_msg_filter_initial(struct gsm48_hdr *hdr, size_t size,
 			struct bsc_filter_reject_cause *cause);
 int bsc_msg_filter_data(struct gsm48_hdr *hdr, size_t size,
 			struct bsc_connection *bsc,
-			struct nat_sccp_connection *con,
+			struct bsc_filter_state *state,
 			struct bsc_filter_reject_cause *cause);
 
 /* IMSI allow/deny handling */
diff --git a/openbsc/include/openbsc/bsc_nat_sccp.h b/openbsc/include/openbsc/bsc_nat_sccp.h
index 0561df1f..d2490ca6 100644
--- a/openbsc/include/openbsc/bsc_nat_sccp.h
+++ b/openbsc/include/openbsc/bsc_nat_sccp.h
@@ -22,6 +22,8 @@
 #ifndef BSC_NAT_SCCP_H
 #define BSC_NAT_SCCP_H
 
+#include "bsc_msg_filter.h"
+
 #include <osmocom/sccp/sccp_types.h>
 
 /*
@@ -80,8 +82,8 @@ struct nat_sccp_connection {
 	int con_type;
 	int con_local;
 	int authorized;
-	int imsi_checked;
-	char *imsi;
+
+	struct bsc_filter_state filter_state;
 
 	uint16_t lac;
 	uint16_t ci;
diff --git a/openbsc/src/libfilter/bsc_msg_filter.c b/openbsc/src/libfilter/bsc_msg_filter.c
index b836f432..52c71b99 100644
--- a/openbsc/src/libfilter/bsc_msg_filter.c
+++ b/openbsc/src/libfilter/bsc_msg_filter.c
@@ -306,9 +306,9 @@ static int _cr_check_pag_resp(void *ctx,
 	return 1;
 }
 
-static int _dt_check_id_resp(struct filter_request *req,
+static int _dt_check_id_resp(void *ctx, struct filter_request *req,
 			     uint8_t *data, unsigned int length,
-			     struct nat_sccp_connection *con,
+			     struct bsc_filter_state *state,
 			     struct bsc_filter_reject_cause *cause)
 {
 	char mi_string[GSM48_MI_SIZE];
@@ -330,8 +330,8 @@ static int _dt_check_id_resp(struct filter_request *req,
 	if (mi_type != GSM_MI_TYPE_IMSI)
 		return 0;
 
-	con->imsi_checked = 1;
-	con->imsi = talloc_strdup(con, mi_string);
+	state->imsi_checked = 1;
+	state->imsi = talloc_strdup(ctx, mi_string);
 	return auth_imsi(req, mi_string, cause);
 }
 
@@ -394,7 +394,7 @@ int bsc_msg_filter_initial(struct gsm48_hdr *hdr48, size_t hdr48_len,
 
 int bsc_msg_filter_data(struct gsm48_hdr *hdr48, size_t len,
 		struct bsc_connection *bsc,
-		struct nat_sccp_connection *con,
+		struct bsc_filter_state *state,
 		struct bsc_filter_reject_cause *cause)
 {
 	struct filter_request req;
@@ -403,7 +403,7 @@ int bsc_msg_filter_data(struct gsm48_hdr *hdr48, size_t len,
 	cause->cm_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;
 	cause->lu_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;
 
-	if (con->imsi_checked)
+	if (state->imsi_checked)
 		return 0;
 
 	proto = hdr48->proto_discr & 0x0f;
@@ -416,6 +416,6 @@ int bsc_msg_filter_data(struct gsm48_hdr *hdr48, size_t len,
 	req.local_lst_name = bsc->cfg->acc_lst_name;
 	req.global_lst_name = bsc->nat->acc_lst_name;
 	req.bsc_nr = bsc->cfg->nr;
-	return _dt_check_id_resp(&req, &hdr48->data[0],
-					len - sizeof(*hdr48), con, cause);
+	return _dt_check_id_resp(bsc, &req, &hdr48->data[0],
+					len - sizeof(*hdr48), state, cause);
 }
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat.c b/openbsc/src/osmo-bsc_nat/bsc_nat.c
index 116c612c..3ec43b15 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat.c
@@ -1073,10 +1073,10 @@ static int forward_sccp_to_msc(struct bsc_connection *bsc, struct msgb *msg)
 			con->msc_con = bsc->nat->msc_con;
 			con_msc = con->msc_con;
 			con->con_type = con_type;
-			con->imsi_checked = filter;
+			con->filter_state.imsi_checked = filter;
 			bsc_nat_extract_lac(bsc, con, parsed, msg);
 			if (imsi)
-				con->imsi = talloc_steal(con, imsi);
+				con->filter_state.imsi = talloc_steal(con, imsi);
 			imsi = NULL;
 			con_bsc = con->bsc;
 			handle_con_stats(con);
@@ -1094,8 +1094,9 @@ static int forward_sccp_to_msc(struct bsc_connection *bsc, struct msgb *msg)
 					filter = bsc_nat_filter_dt(bsc, msg,
 							con, parsed, &cause);
 					if (filter < 0) {
-						if (con->imsi)
-							bsc_nat_inform_reject(bsc, con->imsi);
+						if (con->filter_state.imsi)
+							bsc_nat_inform_reject(bsc,
+								con->filter_state.imsi);
 						bsc_stat_reject(filter, bsc, 1);
 						bsc_send_con_release(bsc, con, &cause);
 						con = NULL;
@@ -1111,7 +1112,8 @@ static int forward_sccp_to_msc(struct bsc_connection *bsc, struct msgb *msg)
 					 * replace the msg and the parsed structure becomes
 					 * invalid.
 					 */
-					msg = bsc_nat_rewrite_msg(bsc->nat, msg, parsed, con->imsi);
+					msg = bsc_nat_rewrite_msg(bsc->nat, msg, parsed,
+									con->filter_state.imsi);
 					talloc_free(parsed);
 					parsed = NULL;
 				} else if (con->con_local == NAT_CON_END_USSD) {
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c b/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c
index 11d370c4..af0f7a18 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c
@@ -90,7 +90,7 @@ int bsc_nat_filter_dt(struct bsc_connection *bsc, struct msgb *msg,
 	cause->cm_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;
 	cause->lu_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;
 
-	if (con->imsi_checked)
+	if (con->filter_state.imsi_checked)
 		return 0;
 
 	/* only care about DTAP messages */
@@ -101,5 +101,5 @@ int bsc_nat_filter_dt(struct bsc_connection *bsc, struct msgb *msg,
 	if (!hdr48)
 		return -1;
 
-	return bsc_msg_filter_data(hdr48, len, bsc, con, cause);
+	return bsc_msg_filter_data(hdr48, len, bsc, &con->filter_state, cause);
 }
diff --git a/openbsc/src/osmo-bsc_nat/bsc_ussd.c b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
index 968456b9..22418960 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_ussd.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
@@ -351,7 +351,7 @@ static int forward_ussd(struct nat_sccp_connection *con, const struct ussd_reque
 	state->invoke_id = req->invoke_id;
 	memcpy(&state->src_ref, &con->remote_ref, sizeof(con->remote_ref));
 	memcpy(&state->dst_ref, &con->real_ref, sizeof(con->real_ref));
-	memcpy(state->imsi, con->imsi, strlen(con->imsi));
+	memcpy(state->imsi, con->filter_state.imsi, strlen(con->filter_state.imsi));
 
 	/* add additional tag/values */
 	lac = htons(con->lac);
@@ -385,7 +385,7 @@ int bsc_ussd_check(struct nat_sccp_connection *con, struct bsc_nat_parsed *parse
 	if (con->con_type != NAT_CON_TYPE_SSA)
 		return 0;
 
-	if (!con->imsi)
+	if (!con->filter_state.imsi)
 		return 0;
 
 	/* We have not verified the IMSI yet */
@@ -400,7 +400,7 @@ int bsc_ussd_check(struct nat_sccp_connection *con, struct bsc_nat_parsed *parse
 	if (parsed->bssap != BSSAP_MSG_DTAP)
 		return 0;
 
-	if (strlen(con->imsi) >= GSM_IMSI_LENGTH)
+	if (strlen(con->filter_state.imsi) >= GSM_IMSI_LENGTH)
 		return 0;
 
 	hdr48 = bsc_unpack_dtap(parsed, msg, &len);
@@ -421,7 +421,7 @@ int bsc_ussd_check(struct nat_sccp_connection *con, struct bsc_nat_parsed *parse
 		if (!lst)
 			return 0;
 
-		if (bsc_msg_acc_lst_check_allow(lst, con->imsi) != 0)
+		if (bsc_msg_acc_lst_check_allow(lst, con->filter_state.imsi) != 0)
 			return 0;
 
 		/* now decode the message and see if we really want to handle it */
@@ -436,14 +436,15 @@ int bsc_ussd_check(struct nat_sccp_connection *con, struct bsc_nat_parsed *parse
 			return 0;
 
 		/* found a USSD query for our subscriber */
-		LOGP(DNAT, LOGL_NOTICE, "Found USSD query for %s\n", con->imsi);
+		LOGP(DNAT, LOGL_NOTICE, "Found USSD query for %s\n",
+			con->filter_state.imsi);
 		con->ussd_ti[ti] = 1;
 		if (forward_ussd(con, &req, msg) != 0)
 			return 0;
 		return 1;
 	} else if (msg_type == GSM0480_MTYPE_FACILITY && con->ussd_ti[ti]) {
 		LOGP(DNAT, LOGL_NOTICE, "Forwarding message part of TI: %d %s\n",
-		     ti, con->imsi);
+		     ti, con->filter_state.imsi);
 		if (forward_ussd_simple(con, msg) != 0)
 			return 0;
 		return 1;
diff --git a/openbsc/tests/bsc-nat/bsc_nat_test.c b/openbsc/tests/bsc-nat/bsc_nat_test.c
index 2020c7ad..e883ddd4 100644
--- a/openbsc/tests/bsc-nat/bsc_nat_test.c
+++ b/openbsc/tests/bsc-nat/bsc_nat_test.c
@@ -992,7 +992,7 @@ static void test_dt_filter()
 		if (!parsed)
 			continue;
 
-		con->imsi_checked = 0;
+		con->filter_state.imsi_checked = 0;
 		memset(&cause, 0, sizeof(cause));
 		bsc_nat_filter_dt(bsc, msg, con, parsed, &cause);
 	}