diff --git a/src/bts.cpp b/src/bts.cpp
index e41b1fa..6bdbb85 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -1619,8 +1619,45 @@
 	return rc;
 }
 
-void bts_update_tbf_ta(const char *p, uint32_t fn, uint8_t trx_no, uint8_t ts,
-		       uint8_t ta)
+/* update TA based on TA provided by PH-DATA-IND */
+void update_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, int8_t ta_delta)
+{
+	int16_t ta_adj;
+	uint8_t ta_target;
+
+	if (ta_delta) {
+		/* adjust TA based on TA provided by PH-DATA-IND */
+		ta_adj = tbf->ta() + ta_delta;
+
+		/* limit target TA in range 0..63 bits */
+		ta_target = ta_limit(ta_adj);
+
+		LOGP(DL1IF, LOGL_INFO, "PH-DATA-IND is updating TLLI=0x%08x: TA %u -> %u on "
+				"TRX = %d, TS = %d, FN = %d\n",
+				tbf->tlli(), tbf->ta(), ta_target,
+				tbf->trx->trx_no , tbf->poll_ts, tbf->poll_fn);
+		tbf->set_ta(ta_target);
+	}
+}
+
+/* set TA based on TA provided by PH-RA-IND */
+void set_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, uint8_t ta)
+{
+	uint8_t ta_target;
+
+	if (tbf->ta() != ta) {
+		/* limit target TA in range 0..63 bits */
+		ta_target = ta_limit(ta);
+
+		LOGP(DL1IF, LOGL_INFO, "PH-RA-IND is updating TLLI=0x%08x: TA %u -> %u on "
+				"TRX = %d, TS = %d, FN = %d\n",
+				tbf->tlli(), tbf->ta(), ta_target,
+				tbf->trx->trx_no , tbf->poll_ts, tbf->poll_fn);
+		tbf->set_ta(ta_target);
+	}
+}
+
+void bts_update_tbf_ta(const char *p, uint32_t fn, uint8_t trx_no, uint8_t ts, int8_t ta, bool is_rach)
 {
 	struct gprs_rlcmac_ul_tbf *tbf =
 		bts_main_data()->bts->ul_tbf_by_poll_fn(fn, trx_no, ts);
@@ -1628,11 +1665,16 @@
 		LOGP(DL1IF, LOGL_DEBUG, "[%s] update TA = %u ignored due to "
 		     "unknown UL TBF on TRX = %d, TS = %d, FN = %d\n",
 		     p, ta, trx_no, ts, fn);
-	else if (tbf->ta() != ta) {
-		LOGP(DL1IF, LOGL_INFO, "[%s] Updating TA %u -> %u on "
-		     "TRX = %d, TS = %d, FN = %d\n",
-		     p, tbf->ta(), ta, trx_no, ts, fn);
-		tbf->set_ta(ta);
+	else {
+		/* we need to distinguish TA information provided by L1
+		 * from PH-DATA-IND and PHY-RA-IND so that we can properly
+		 * update TA for given TBF
+		 */
+		if (is_rach)
+			set_tbf_ta(tbf, (uint8_t)ta);
+		else
+			update_tbf_ta(tbf, ta);
+
 	}
 }
 
diff --git a/src/bts.h b/src/bts.h
index d65cd2f..aaf81cf 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -162,8 +162,9 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-void bts_update_tbf_ta(const char *p, uint32_t fn, uint8_t trx_no, uint8_t ts,
-		       uint8_t ta);
+void bts_update_tbf_ta(const char *p, uint32_t fn, uint8_t trx_no, uint8_t ts, int8_t ta, bool is_rach);
+void update_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, int8_t ta_delta);
+void set_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, uint8_t ta);
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/osmo-bts-litecell15/lc15_l1_if.c b/src/osmo-bts-litecell15/lc15_l1_if.c
index 37b7f78..8290a93 100644
--- a/src/osmo-bts-litecell15/lc15_l1_if.c
+++ b/src/osmo-bts-litecell15/lc15_l1_if.c
@@ -203,7 +203,7 @@
 
 	get_meas(&meas, &data_ind->measParam);
 	bts_update_tbf_ta("PH-DATA", data_ind->u32Fn, fl1h->trx_no,
-			  data_ind->u8Tn, qta2ta(meas.bto));
+			  data_ind->u8Tn, sign_qta2ta(meas.bto), false);
 
 	switch (data_ind->sapi) {
 	case GsmL1_Sapi_Pdtch:
@@ -248,7 +248,7 @@
 
 	DEBUGP(DL1IF, "Rx PH-RA.ind");
 	bts_update_tbf_ta("PH-RA", ra_ind->u32Fn, fl1h->trx_no, ra_ind->u8Tn,
-			  qta2ta(ra_ind->measParam.i16BurstTiming));
+			qta2ta(ra_ind->measParam.i16BurstTiming), true);
 
 	return 0;
 }
diff --git a/src/osmo-bts-sysmo/sysmo_l1_if.c b/src/osmo-bts-sysmo/sysmo_l1_if.c
index 1c5ecc9..dfef239 100644
--- a/src/osmo-bts-sysmo/sysmo_l1_if.c
+++ b/src/osmo-bts-sysmo/sysmo_l1_if.c
@@ -188,7 +188,7 @@
 
 	get_meas(&meas, &data_ind->measParam);
 	bts_update_tbf_ta("PH-DATA", data_ind->u32Fn, fl1h->trx_no,
-			  data_ind->u8Tn, qta2ta(meas.bto));
+			  data_ind->u8Tn, sign_qta2ta(meas.bto), false);
 
 	switch (data_ind->sapi) {
 	case GsmL1_Sapi_Pdtch:
@@ -237,7 +237,7 @@
 
 	DEBUGP(DL1IF, "Rx PH-RA.ind");
 	bts_update_tbf_ta("PH-RA", ra_ind->u32Fn, fl1h->trx_no, ra_ind->u8Tn,
-			  qta2ta(ra_ind->measParam.i16BurstTiming));
+			qta2ta(ra_ind->measParam.i16BurstTiming), true);
 
 	return 0;
 }
diff --git a/src/pcu_l1_if.h b/src/pcu_l1_if.h
index 1618260..cb2a6df 100644
--- a/src/pcu_l1_if.h
+++ b/src/pcu_l1_if.h
@@ -43,6 +43,34 @@
 	return qta >> 2;
 }
 
+static inline int8_t sign_qta2ta(int16_t qta)
+{
+	int8_t ta_adj = 0;
+
+	if (qta < -252)
+		qta = -252;
+
+	if (qta > 252)
+		qta = 252;
+
+	/* 1-bit TA adjustment  if TA error reported by L1 is outside +/- 2 qbits */
+	if (qta > 2)
+		ta_adj = 1;
+	if (qta < -2)
+		ta_adj = -1;
+
+	return (qta >> 2) + ta_adj;
+}
+
+static inline uint8_t ta_limit(int16_t ta)
+{
+	if (ta < 0)
+		ta = 0;
+	if (ta > 63)
+		ta = 63;
+	return ta;
+}
+
 /*
  * L1 Measurement values
  */