diff --git a/src/gprs_ms.c b/src/gprs_ms.c
index 073dd4a7..29d226fa 100644
--- a/src/gprs_ms.c
+++ b/src/gprs_ms.c
@@ -120,7 +120,6 @@ struct GprsMs *ms_alloc(struct gprs_rlcmac_bts *bts, uint32_t tlli)
 	ms->current_cs_ul = UNKNOWN;
 	ms->current_cs_dl = UNKNOWN;
 	ms->is_idle = true;
-	ms->first_common_ts = TBF_TS_UNSET;
 	INIT_LLIST_HEAD(&ms->list);
 	INIT_LLIST_HEAD(&ms->old_tbfs);
 
@@ -384,7 +383,7 @@ void ms_detach_tbf(struct GprsMs *ms, struct gprs_rlcmac_tbf *tbf)
 
 	if (!ms->dl_tbf && !ms->ul_tbf) {
 		ms_set_reserved_slots(ms, NULL, 0, 0);
-		ms->first_common_ts = TBF_TS_UNSET;
+		ms->first_common_ts = NULL;
 
 		if (ms_tlli(ms) != 0)
 			ms_release_timer_start(ms);
@@ -920,15 +919,15 @@ enum CodingScheme ms_current_cs_dl(const struct GprsMs *ms, enum mcs_kind req_mc
 	return cs;
 }
 
-int8_t ms_first_common_ts(const struct GprsMs *ms)
+struct gprs_rlcmac_pdch *ms_first_common_ts(const struct GprsMs *ms)
 {
 	return ms->first_common_ts;
 }
 
-void ms_set_first_common_ts(struct GprsMs *ms, uint8_t first_common_ts)
+void ms_set_first_common_ts(struct GprsMs *ms, struct gprs_rlcmac_pdch *pdch)
 {
-	OSMO_ASSERT(first_common_ts < 8);
-	ms->first_common_ts = first_common_ts;
+	OSMO_ASSERT(pdch);
+	ms->first_common_ts = pdch;
 }
 
 uint8_t ms_dl_slots(const struct GprsMs *ms)
diff --git a/src/gprs_ms.h b/src/gprs_ms.h
index 92292e39..835ff186 100644
--- a/src/gprs_ms.h
+++ b/src/gprs_ms.h
@@ -64,8 +64,8 @@ struct GprsMs {
 	struct gprs_rlcmac_ul_tbf *ul_tbf;
 	struct gprs_rlcmac_dl_tbf *dl_tbf;
 	struct llist_head old_tbfs; /* list of gprs_rlcmac_tbf */
-	/* First common timeslot number used both in UL and DL, 0..7 or TBF_TS_UNSET (-1): */
-	int8_t first_common_ts;
+	/* First common timeslot used both in UL and DL, or NULL if not set: */
+	struct gprs_rlcmac_pdch *first_common_ts;
 
 	uint32_t tlli;
 	uint32_t new_ul_tlli;
@@ -103,8 +103,8 @@ struct GprsMs {
 
 struct GprsMs *ms_alloc(struct gprs_rlcmac_bts *bts, uint32_t tlli);
 
-int8_t ms_first_common_ts(const struct GprsMs *ms);
-void ms_set_first_common_ts(struct GprsMs *ms, uint8_t first_common_ts);
+struct gprs_rlcmac_pdch *ms_first_common_ts(const struct GprsMs *ms);
+void ms_set_first_common_ts(struct GprsMs *ms, struct gprs_rlcmac_pdch *pdch);
 void ms_set_reserved_slots(struct GprsMs *ms, struct gprs_rlcmac_trx *trx,
 			   uint8_t ul_slots, uint8_t dl_slots);
 struct GprsMs *ms_ref(struct GprsMs *ms);
diff --git a/src/gprs_rlcmac_ts_alloc.cpp b/src/gprs_rlcmac_ts_alloc.cpp
index 96098a9c..704b6960 100644
--- a/src/gprs_rlcmac_ts_alloc.cpp
+++ b/src/gprs_rlcmac_ts_alloc.cpp
@@ -350,6 +350,7 @@ int alloc_algorithm_a(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 	const char *mask_reason = NULL;
 	struct GprsMs *ms = tbf->ms();
 	gprs_rlcmac_trx *trx = ms_current_trx(ms);
+	struct gprs_rlcmac_pdch *first_common_ts = ms_first_common_ts(ms);
 
 	LOGPAL(tbf, "A", single, use_trx, LOGL_DEBUG, "Alloc start\n");
 
@@ -365,11 +366,9 @@ int alloc_algorithm_a(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 	dl_slots = ms_reserved_dl_slots(ms);
 	ul_slots = ms_reserved_ul_slots(ms);
 
-	ts = ms_first_common_ts(ms);
-
-	if (ts >= 0) {
+	if (first_common_ts) {
 		mask_reason = "need to reuse TS";
-		mask = 1 << ts;
+		mask = 1 << first_common_ts->ts_no;
 	} else if (dl_slots || ul_slots) {
 		mask_reason = "need to use a reserved common TS";
 		mask = dl_slots & ul_slots;
@@ -412,7 +411,7 @@ int alloc_algorithm_a(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 	tbf->trx = trx;
 	/* the only one TS is the common TS */
 	ms_set_reserved_slots(ms, trx, 1 << ts, 1 << ts);
-	ms_set_first_common_ts(ms, ts);
+	ms_set_first_common_ts(ms, pdch);
 
 	tbf->upgrade_to_multislot = false;
 	bts_do_rate_ctr_inc(bts, CTR_TBF_ALLOC_ALGO_A);
@@ -861,7 +860,7 @@ int alloc_algorithm_b(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 	uint8_t ul_slots;
 	uint8_t reserved_dl_slots;
 	uint8_t reserved_ul_slots;
-	int8_t first_common_ts;
+	int8_t first_common_tn;
 	uint8_t slotcount = 0;
 	uint8_t reserve_count = 0, trx_no;
 	int first_ts;
@@ -870,6 +869,7 @@ int alloc_algorithm_b(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 	int tfi;
 	struct GprsMs *ms = tbf->ms();
 	gprs_rlcmac_trx *trx;
+	struct gprs_rlcmac_pdch *first_common_ts = ms_first_common_ts(ms);
 
 	LOGPAL(tbf, "B", single, use_trx, LOGL_DEBUG, "Alloc start\n");
 
@@ -877,7 +877,7 @@ int alloc_algorithm_b(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 
 	reserved_dl_slots = ms_reserved_dl_slots(ms);
 	reserved_ul_slots = ms_reserved_ul_slots(ms);
-	first_common_ts = ms_first_common_ts(ms);
+	first_common_tn = first_common_ts ? first_common_ts->ts_no : -1;
 
 	/* Step 2a: Find usable TRX and TFI */
 	tfi = tfi_find_free(bts, ms, tbf->direction, use_trx, &trx_no);
@@ -899,7 +899,7 @@ int alloc_algorithm_b(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 
 	/* Step 3a: Derive the slot set for the current TBF */
 	rc = tbf_select_slot_set(tbf, trx, single, ul_slots, dl_slots, reserved_ul_slots, reserved_dl_slots,
-				 first_common_ts);
+				 first_common_tn);
 	if (rc < 0)
 		return -EINVAL;
 
@@ -924,11 +924,12 @@ int alloc_algorithm_b(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf,
 		return -EINVAL;
 	}
 
-	first_common_ts = ffs(dl_slots & ul_slots) - 1;
-	if (first_common_ts < 0) {
+	first_common_tn = ffs(dl_slots & ul_slots) - 1;
+	if (first_common_tn < 0) {
 		LOGPAL(tbf, "B", single, use_trx, LOGL_NOTICE, "first common slot unavailable\n");
 		return -EINVAL;
 	}
+	first_common_ts = &trx->pdch[first_common_tn];
 
 	if (single && slotcount) {
 		tbf->upgrade_to_multislot = (reserve_count > slotcount);
diff --git a/src/pcu_vty_functions.cpp b/src/pcu_vty_functions.cpp
index 17aa2038..facc34c9 100644
--- a/src/pcu_vty_functions.cpp
+++ b/src/pcu_vty_functions.cpp
@@ -55,6 +55,7 @@ static void tbf_print_vty_info(struct vty *vty, struct gprs_rlcmac_tbf *tbf)
 	gprs_rlcmac_dl_tbf *dl_tbf = tbf_as_dl_tbf(tbf);
 	uint32_t state_flags = tbf_state_flags(tbf);
 	struct GprsMs *ms = tbf_ms(tbf);
+	const struct gprs_rlcmac_pdch *first_common_ts = ms_first_common_ts(ms);
 
 	vty_out(vty, "TBF: TFI=%d TLLI=0x%08x (%s) TA=%u DIR=%s IMSI=%s%s", tbf->tfi(),
 		tbf->tlli(), tbf->is_tlli_valid() ? "valid" : "invalid",
@@ -66,7 +67,8 @@ static void tbf_print_vty_info(struct vty *vty, struct gprs_rlcmac_tbf *tbf)
 		state_flags,
 		state_flags & (1 << GPRS_RLCMAC_FLAG_CCCH),
 		state_flags & (1 << GPRS_RLCMAC_FLAG_PACCH),
-		ms_first_common_ts(ms), tbf->control_ts,
+		first_common_ts ? first_common_ts->ts_no : -1,
+		tbf->control_ts,
 		tbf->ms_class(),
 		ms_egprs_ms_class(ms),
 		VTY_NEWLINE);
diff --git a/src/tbf.cpp b/src/tbf.cpp
index 2cc60539..c934f078 100644
--- a/src/tbf.cpp
+++ b/src/tbf.cpp
@@ -279,14 +279,15 @@ uint16_t egprs_window_size(const struct gprs_rlcmac_bts *bts, uint8_t slots)
 
 void tbf_assign_control_ts(struct gprs_rlcmac_tbf *tbf)
 {
-	int8_t first_common_ts = ms_first_common_ts(tbf_ms(tbf));
+	struct gprs_rlcmac_pdch *first_common = ms_first_common_ts(tbf_ms(tbf));
+	OSMO_ASSERT(first_common);
 	if (tbf->control_ts == TBF_TS_UNSET)
 		LOGPTBF(tbf, LOGL_INFO, "Setting Control TS %d\n",
-			first_common_ts);
-	else if (tbf->control_ts != first_common_ts)
+			first_common->ts_no);
+	else if (tbf->control_ts != first_common->ts_no)
 		LOGPTBF(tbf, LOGL_INFO, "Changing Control TS %d -> %d\n",
-			tbf->control_ts, first_common_ts);
-	tbf->control_ts = first_common_ts;
+			tbf->control_ts, first_common->ts_no);
+	tbf->control_ts = first_common->ts_no;
 }
 
 void gprs_rlcmac_tbf::n_reset(enum tbf_counters n)
@@ -706,13 +707,14 @@ uint8_t gprs_rlcmac_tbf::ul_slots() const
 {
 	uint8_t slots = 0;
 	size_t i;
+	struct gprs_rlcmac_pdch *first_common;
 
 	if (direction == GPRS_RLCMAC_DL_TBF) {
 		if (control_ts < 8)
 			slots |= 1 << control_ts;
-		int8_t first_common_ts = ms_first_common_ts(tbf_ms(this));
-		if (first_common_ts != TBF_TS_UNSET)
-			slots |= 1 << first_common_ts;
+		first_common = ms_first_common_ts(tbf_ms(this));
+		if (first_common)
+			slots |= 1 << first_common->ts_no;
 
 		return slots;
 	}
diff --git a/src/tbf_ul.cpp b/src/tbf_ul.cpp
index b04c5117..a0e03985 100644
--- a/src/tbf_ul.cpp
+++ b/src/tbf_ul.cpp
@@ -166,7 +166,7 @@ struct gprs_rlcmac_ul_tbf *ul_tbf_alloc_rejected(struct gprs_rlcmac_bts *bts, st
 
 	ul_tbf->trx = trx;
 	/* The only one TS is the common, control TS */
-	ms_set_first_common_ts(ms, pdch->ts_no);
+	ms_set_first_common_ts(ms, pdch);
 	tbf_assign_control_ts(ul_tbf);
 	ul_tbf->m_ctrs = rate_ctr_group_alloc(ul_tbf, &tbf_ctrg_desc, next_tbf_ctr_group_id++);
 	ul_tbf->m_ul_egprs_ctrs = rate_ctr_group_alloc(ul_tbf,
diff --git a/tests/alloc/AllocTest.cpp b/tests/alloc/AllocTest.cpp
index 215a7aed..4b4fbd5d 100644
--- a/tests/alloc/AllocTest.cpp
+++ b/tests/alloc/AllocTest.cpp
@@ -177,12 +177,13 @@ static void dump_assignment(struct gprs_rlcmac_tbf *tbf, const char *dir, bool v
 	if (!verbose)
 		return;
 	const struct GprsMs *ms = tbf_ms(tbf);
+	const struct gprs_rlcmac_pdch *first_common = ms_first_common_ts(ms);
 
 	for (size_t i = 0; i < ARRAY_SIZE(tbf->pdch); ++i)
 		if (tbf->pdch[i])
 			printf("PDCH[%zu] is used for %s\n", i, dir);
 	printf("PDCH[%d] is control_ts for %s\n", tbf->control_ts, dir);
-	printf("PDCH[%d] is first common for %s\n", ms_first_common_ts(ms), dir);
+	printf("PDCH[%d] is first common for %s\n", first_common ? first_common->ts_no : -1, dir);
 }
 
 #define ENABLE_PDCH(ts_no, enable_flag, trx)	\
@@ -569,13 +570,13 @@ static unsigned alloc_many_tbfs(struct gprs_rlcmac_bts *bts, unsigned min_class,
 		trx = ms_current_trx(ms);
 
 		OSMO_ASSERT(ul_tbf || dl_tbf);
-		OSMO_ASSERT(ms_first_common_ts(ms) != TBF_TS_UNSET);
+		OSMO_ASSERT(ms_first_common_ts(ms) != NULL);
 		if (ul_tbf) {
-			ul_slots = 1 << (uint8_t)ms_first_common_ts(ms);
+			ul_slots = 1 << (uint8_t)ms_first_common_ts(ms)->ts_no;
 			tfi = ul_tbf->tfi();
 			dir = GPRS_RLCMAC_UL_TBF;
 		} else {
-			ul_slots = 1 << (uint8_t)ms_first_common_ts(ms);
+			ul_slots = 1 << (uint8_t)ms_first_common_ts(ms)->ts_no;
 			tfi = dl_tbf->tfi();
 			dir = GPRS_RLCMAC_DL_TBF;
 		}
diff --git a/tests/ulc/PdchUlcTest.cpp b/tests/ulc/PdchUlcTest.cpp
index 2501f609..a1993115 100644
--- a/tests/ulc/PdchUlcTest.cpp
+++ b/tests/ulc/PdchUlcTest.cpp
@@ -169,6 +169,7 @@ int _alloc_algorithm_dummy(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *
 			   bool single, int8_t use_tbf)
 {
 	tbf->trx = &bts->trx[0];
+	ms_set_first_common_ts(tbf_ms(tbf), &tbf->trx->pdch[0]);
 	return 0;
 }