diff --git a/include/osmocom/gprs/gmm/gmm_ms_fsm.h b/include/osmocom/gprs/gmm/gmm_ms_fsm.h
index 516801e..078c535 100644
--- a/include/osmocom/gprs/gmm/gmm_ms_fsm.h
+++ b/include/osmocom/gprs/gmm/gmm_ms_fsm.h
@@ -48,9 +48,6 @@ struct gprs_gmm_ms_fsm_attach_ctx {
 	bool with_imsi;
 	bool explicit_att; /* true if by SMREG-ATTACH.req requested it */
 	bool implicit_att; /* true if GMMSM-ESTABLISH.req requested it */
-	/* Session Ids waiting for attach to happen during implicit_att: */
-	uint32_t sess_id[16];
-	uint8_t num_sess_id;
 	/* Retransmission of ATTACH REQUEST (T3310) */
 	uint8_t req_attempts;
 };
@@ -78,8 +75,7 @@ void gprs_gmm_ms_fsm_ctx_release(struct gprs_gmm_ms_fsm_ctx *ctx);
 int gprs_gmm_ms_fsm_ctx_request_attach(struct gprs_gmm_ms_fsm_ctx *ctx,
 				       enum osmo_gprs_gmm_attach_type attach_type,
 				       bool attach_with_imsi,
-				       bool explicit_attach,
-				       uint32_t sess_id);
+				       bool explicit_attach);
 
 int gprs_gmm_ms_fsm_ctx_request_detach(struct gprs_gmm_ms_fsm_ctx *ctx,
 				       enum osmo_gprs_gmm_detach_ms_type detach_type,
diff --git a/include/osmocom/gprs/gmm/gmm_private.h b/include/osmocom/gprs/gmm/gmm_private.h
index bdff1c1..6abf3be 100644
--- a/include/osmocom/gprs/gmm/gmm_private.h
+++ b/include/osmocom/gprs/gmm/gmm_private.h
@@ -20,6 +20,8 @@
 /* 3GPP TS 44.064 § 8.3 TLLI assignment procedures */
 #define GPRS_GMM_TLLI_UNASSIGNED (0xffffffff)
 
+#define GPRS_GMM_SESS_ID_UNASSIGNED (0xffffffff)
+
 extern int g_gmm_log_cat[_OSMO_GPRS_GMM_LOGC_MAX];
 
 #define LOGGMM(lvl, fmt, args...) LOGP(g_gmm_log_cat[OSMO_GPRS_GMM_LOGC_GMM], lvl, fmt, ## args)
@@ -53,6 +55,7 @@ struct gprs_gmm_entity {
 	struct llist_head list; /* item in (struct gprs_gmm_ctx)->gmme_list */
 
 	struct gprs_gmm_ms_fsm_ctx ms_fsm;
+	uint32_t sess_id; /* Used to identify the GMME in GMMSM SAP */
 	uint32_t ptmsi;
 	uint32_t old_ptmsi;
 	uint32_t tlli;
diff --git a/src/gmm/gmm.c b/src/gmm/gmm.c
index 8f54f04..980f8f4 100644
--- a/src/gmm/gmm.c
+++ b/src/gmm/gmm.c
@@ -149,6 +149,7 @@ struct gprs_gmm_entity *gprs_gmm_gmme_alloc(uint32_t ptmsi, const char *imsi)
 		return NULL;
 	}
 
+	gmme->sess_id = GPRS_GMM_SESS_ID_UNASSIGNED;
 	gmme->ptmsi = ptmsi;
 	gmme->old_ptmsi = GSM_RESERVED_TMSI;
 	gmme->old_tlli = GPRS_GMM_TLLI_UNASSIGNED;
diff --git a/src/gmm/gmm_ms_fsm.c b/src/gmm/gmm_ms_fsm.c
index 85aa6bf..6f82815 100644
--- a/src/gmm/gmm_ms_fsm.c
+++ b/src/gmm/gmm_ms_fsm.c
@@ -132,14 +132,11 @@ static void st_gmm_ms_registered_initiated(struct osmo_fsm_inst *fi, uint32_t ev
 
 		if (att.implicit_att) {
 			/* Submit GMMSM-ESTABLISH-CNF as per TS 24.007 Annex C.3 */
-			unsigned int i;
-			for (i = 0; i < att.num_sess_id; i++) {
-				rc = gprs_gmm_submit_gmmsm_establish_cnf(ctx->gmme,
-									 att.sess_id[i],
-									 false, cause);
-				if (rc < 0)
-					return;
-			}
+			rc = gprs_gmm_submit_gmmsm_establish_cnf(ctx->gmme,
+								 ctx->gmme->sess_id,
+								 false, cause);
+			if (rc < 0)
+				return;
 		}
 		break;
 	case GPRS_GMM_MS_EV_ATTACH_ACCEPTED:
@@ -153,12 +150,9 @@ static void st_gmm_ms_registered_initiated(struct osmo_fsm_inst *fi, uint32_t ev
 		}
 		if (ctx->attach.implicit_att) {
 			/* Submit GMMSM-ESTABLISH-CNF as per TS 24.007 Annex C.3 */
-			unsigned int i;
-			for (i = 0; i < ctx->attach.num_sess_id; i++) {
-				rc = gprs_gmm_submit_gmmsm_establish_cnf(ctx->gmme, ctx->attach.sess_id[i], true, 0);
-				if (rc < 0)
-					return;
-			}
+			rc = gprs_gmm_submit_gmmsm_establish_cnf(ctx->gmme, ctx->gmme->sess_id, true, 0);
+			if (rc < 0)
+				return;
 		}
 		break;
 	case GPRS_GMM_MS_EV_DETACH_REQUESTED:
@@ -419,8 +413,7 @@ void gprs_gmm_ms_fsm_ctx_release(struct gprs_gmm_ms_fsm_ctx *ctx)
 int gprs_gmm_ms_fsm_ctx_request_attach(struct gprs_gmm_ms_fsm_ctx *ctx,
 				       enum osmo_gprs_gmm_attach_type attach_type,
 				       bool attach_with_imsi,
-				       bool explicit_attach,
-				       uint32_t sess_id)
+				       bool explicit_attach)
 {
 	int rc;
 
@@ -431,23 +424,6 @@ int gprs_gmm_ms_fsm_ctx_request_attach(struct gprs_gmm_ms_fsm_ctx *ctx,
 	else
 		ctx->attach.implicit_att = true;
 
-	if (!explicit_attach) {
-		unsigned int i;
-		bool found = false;
-		if (ctx->attach.num_sess_id == ARRAY_SIZE(ctx->attach.sess_id))
-			return -ENOMEM;
-		for (i = 0; i < ctx->attach.num_sess_id; i++) {
-			if (sess_id == ctx->attach.sess_id[i]) {
-				found = true;
-				break;
-			}
-		}
-		if (!found) {
-			ctx->attach.sess_id[ctx->attach.num_sess_id] = sess_id;
-			ctx->attach.num_sess_id++;
-		}
-	}
-
 	rc = osmo_fsm_inst_dispatch(ctx->fi, GPRS_GMM_MS_EV_ATTACH_REQUESTED, NULL);
 	return rc;
 }
diff --git a/src/gmm/gmm_prim.c b/src/gmm/gmm_prim.c
index 2d53a0a..8f8d218 100644
--- a/src/gmm/gmm_prim.c
+++ b/src/gmm/gmm_prim.c
@@ -389,7 +389,7 @@ static int gprs_gmm_prim_handle_gmmreg_attach_req(struct osmo_gprs_gmm_prim *gmm
 	rc = gprs_gmm_ms_fsm_ctx_request_attach(&gmme->ms_fsm,
 						gmm_prim->gmmreg.attach_req.attach_type,
 						gmm_prim->gmmreg.attach_req.attach_with_imsi,
-						true, 0);
+						true);
 	return rc;
 }
 
@@ -485,6 +485,8 @@ static int gprs_gmm_prim_handle_gmmsm_establish_req(struct osmo_gprs_gmm_prim *g
 	gmme = gprs_gmm_gmme_find_or_create_by_ptmsi_imsi(gmm_prim->gmmsm.establish_req.ptmsi,
 							  gmm_prim->gmmsm.establish_req.imsi);
 	OSMO_ASSERT(gmme);
+	/* Identify this GMME with this sess_id in GMMSM SAP from now on: */
+	gmme->sess_id = gmm_prim->gmmsm.sess_id;
 
 	if (gmme->ms_fsm.fi->state == GPRS_GMM_MS_ST_REGISTERED) {
 		rc = gprs_gmm_submit_gmmsm_establish_cnf(gmme, gmm_prim->gmmsm.sess_id, true, 0);
@@ -499,8 +501,7 @@ static int gprs_gmm_prim_handle_gmmsm_establish_req(struct osmo_gprs_gmm_prim *g
 	rc = gprs_gmm_ms_fsm_ctx_request_attach(&gmme->ms_fsm,
 						gmm_prim->gmmsm.establish_req.attach_type,
 						gmm_prim->gmmsm.establish_req.attach_with_imsi,
-						false,
-						gmm_prim->gmmsm.sess_id);
+						false);
 	return rc;
 }