diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h
index fef2fdd1e..56abfd5c0 100644
--- a/include/osmocom/gsm/gsm_utils.h
+++ b/include/osmocom/gsm/gsm_utils.h
@@ -33,6 +33,7 @@
 	} while (0)
 
 #define GSM_MAX_FN	(26*51*2048)
+#define OSMO_FN_UNSET 0xFFFFFFFF
 
 /* Max length of random identifier which can be requested via osmo_get_rand_id() */
 #define OSMO_MAX_RAND_ID_LEN 16
diff --git a/include/osmocom/gsm/lapd_core.h b/include/osmocom/gsm/lapd_core.h
index 3f31881d3..85e53563b 100644
--- a/include/osmocom/gsm/lapd_core.h
+++ b/include/osmocom/gsm/lapd_core.h
@@ -148,6 +148,7 @@ struct lapd_datalink {
 	int seq_err_cond; /*!< condition of sequence error */
 	uint8_t own_busy; /*!< receiver busy on our side */
 	uint8_t peer_busy; /*!< receiver busy on remote side */
+	uint32_t t200_fn; /*!< Frame Number for computing T200 timer */
 	int t200_sec, t200_usec; /*!< retry timer (default 1 sec) */
 	int t203_sec, t203_usec; /*!< retry timer (default 10 secs) */
 	struct osmo_timer_list t200; /*!< T200 timer */
diff --git a/src/gsm/lapd_core.c b/src/gsm/lapd_core.c
index 9a4f56b96..7e0dfaecb 100644
--- a/src/gsm/lapd_core.c
+++ b/src/gsm/lapd_core.c
@@ -80,6 +80,7 @@
 #include <osmocom/core/utils.h>
 #include <osmocom/core/talloc.h>
 #include <osmocom/gsm/lapd_core.h>
+#include <osmocom/gsm/gsm_utils.h>
 #include <osmocom/gsm/rsl.h>
 
 /* TS 04.06 Table 4 / Section 3.8.1 */
@@ -201,8 +202,8 @@ static void lapd_start_t200(struct lapd_datalink *dl)
 {
 	if (osmo_timer_pending(&dl->t200))
 		return;
-	LOGDL(dl, LOGL_INFO, "start T200 (timeout=%d.%06ds)\n",
-	      dl->t200_sec, dl->t200_usec);
+	LOGDL(dl, LOGL_INFO, "[FN=%u] start T200 (timeout=%d.%06ds)\n",
+	      dl->t200_fn, dl->t200_sec, dl->t200_usec);
 	osmo_timer_schedule(&dl->t200, dl->t200_sec, dl->t200_usec);
 }
 
@@ -218,7 +219,7 @@ static void lapd_stop_t200(struct lapd_datalink *dl)
 {
 	if (!osmo_timer_pending(&dl->t200))
 		return;
-	LOGDL(dl, LOGL_INFO, "stop T200\n");
+	LOGDL(dl, LOGL_INFO, "[FN=%u] stop T200\n", dl->t200_fn);
 	osmo_timer_del(&dl->t200);
 }
 
diff --git a/src/gsm/lapdm.c b/src/gsm/lapdm.c
index e7d46e631..f68254b96 100644
--- a/src/gsm/lapdm.c
+++ b/src/gsm/lapdm.c
@@ -698,7 +698,7 @@ static int lapdm_rx_not_permitted(const struct lapdm_entity *le,
 }
 
 /* input into layer2 (from layer 1) */
-static int l2_ph_data_ind(struct msgb *msg, struct lapdm_entity *le,
+static int l2_ph_data_ind(struct msgb *msg, struct lapdm_entity *le, uint32_t fn,
 	uint8_t chan_nr, uint8_t link_id)
 {
 	uint8_t cbits = chan_nr >> 3;
@@ -762,6 +762,7 @@ static int l2_ph_data_ind(struct msgb *msg, struct lapdm_entity *le,
 	case LAPDm_FMT_B:
 	case LAPDm_FMT_B4:
 		lctx.dl = &mctx.dl->dl;
+		lctx.dl->t200_fn = fn;
 		/* obtain SAPI from address field */
 		mctx.link_id |= LAPDm_ADDR_SAPI(msg->l2h[0]);
 		/* G.2.3 EA bit set to "0" is not allowed in GSM */
@@ -907,7 +908,7 @@ int lapdm_phsap_up(struct osmo_prim_hdr *oph, struct lapdm_entity *le)
 			rc = -ENODEV;
 			goto free;
 		}
-		rc = l2_ph_data_ind(oph->msg, le, pp->u.data.chan_nr,
+		rc = l2_ph_data_ind(oph->msg, le, pp->u.data.fn, pp->u.data.chan_nr,
 				    pp->u.data.link_id);
 		break;
 	case PRIM_PH_RTS: