diff --git a/openbsc/src/gprs/gb_proxy_tlli.c b/openbsc/src/gprs/gb_proxy_tlli.c
index 138837e..467006e 100644
--- a/openbsc/src/gprs/gb_proxy_tlli.c
+++ b/openbsc/src/gprs/gb_proxy_tlli.c
@@ -557,9 +557,14 @@
 		/* A new P-TMSI has been signalled in the message,
 		 * register new TLLI */
 		uint32_t new_sgsn_ptmsi;
-		uint32_t new_bss_ptmsi;
+		uint32_t new_bss_ptmsi = GSM_RESERVED_TMSI;
 		gprs_parse_tmsi(parse_ctx->new_ptmsi_enc, &new_sgsn_ptmsi);
-		new_bss_ptmsi = gbproxy_make_bss_ptmsi(peer, new_sgsn_ptmsi);
+
+		if (link_info->sgsn_tlli.ptmsi == new_sgsn_ptmsi)
+			new_bss_ptmsi = link_info->tlli.ptmsi;
+
+		if (new_bss_ptmsi == GSM_RESERVED_TMSI)
+			new_bss_ptmsi = gbproxy_make_bss_ptmsi(peer, new_sgsn_ptmsi);
 
 		LOGP(DGPRS, LOGL_INFO,
 		     "Got new PTMSI %08x from SGSN, using %08x for BSS\n",
diff --git a/openbsc/tests/gbproxy/gbproxy_test.c b/openbsc/tests/gbproxy/gbproxy_test.c
index f99924c..103b4bd 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.c
+++ b/openbsc/tests/gbproxy/gbproxy_test.c
@@ -2530,11 +2530,11 @@
 
 	link_info = gbproxy_link_info_by_sgsn_tlli(peer, random_sgsn_tlli, SGSN_NSEI);
 	OSMO_ASSERT(link_info);
-	/* OSMO_ASSERT(link_info->tlli.assigned == local_bss_tlli); */
+	OSMO_ASSERT(link_info->tlli.assigned == local_bss_tlli);
 	OSMO_ASSERT(link_info->tlli.current == foreign_bss_tlli);
 	OSMO_ASSERT(!link_info->tlli.bss_validated);
 	OSMO_ASSERT(!link_info->tlli.net_validated);
-	/* OSMO_ASSERT(link_info->tlli.ptmsi == bss_ptmsi); */
+	OSMO_ASSERT(link_info->tlli.ptmsi == bss_ptmsi);
 	OSMO_ASSERT(link_info->sgsn_tlli.assigned == local_sgsn_tlli);
 	OSMO_ASSERT(link_info->sgsn_tlli.current == random_sgsn_tlli);
 	OSMO_ASSERT(!link_info->sgsn_tlli.bss_validated);
@@ -2550,13 +2550,13 @@
 
 	link_info = gbproxy_link_info_by_sgsn_tlli(peer, local_sgsn_tlli, SGSN_NSEI);
 	OSMO_ASSERT(link_info);
-	/* OSMO_ASSERT(link_info->tlli.assigned == local_bss_tlli); */
+	OSMO_ASSERT(link_info->tlli.assigned == local_bss_tlli);
 	OSMO_ASSERT(link_info->tlli.current == foreign_bss_tlli);
-	/* OSMO_ASSERT(link_info->tlli.bss_validated); */
+	OSMO_ASSERT(link_info->tlli.bss_validated);
 	OSMO_ASSERT(!link_info->tlli.net_validated);
 	OSMO_ASSERT(link_info->sgsn_tlli.assigned == local_sgsn_tlli);
 	OSMO_ASSERT(link_info->sgsn_tlli.current == random_sgsn_tlli);
-	/* OSMO_ASSERT(link_info->sgsn_tlli.bss_validated); */
+	OSMO_ASSERT(link_info->sgsn_tlli.bss_validated);
 	OSMO_ASSERT(!link_info->sgsn_tlli.net_validated);
 
 	send_llc_dl_ui(nsi, "GMM INFO", &sgsn_peer, 0x1002,
@@ -2568,10 +2568,10 @@
 
 	link_info = gbproxy_link_info_by_sgsn_tlli(peer, local_sgsn_tlli, SGSN_NSEI);
 	OSMO_ASSERT(link_info);
-	/* OSMO_ASSERT(link_info->tlli.current == local_bss_tlli); */
-	/* OSMO_ASSERT(link_info->tlli.assigned == 0); */
-	/* OSMO_ASSERT(link_info->sgsn_tlli.current == local_sgsn_tlli); */
-	/* OSMO_ASSERT(link_info->sgsn_tlli.assigned == 0); */
+	OSMO_ASSERT(link_info->tlli.current == local_bss_tlli);
+	OSMO_ASSERT(link_info->tlli.assigned == 0);
+	OSMO_ASSERT(link_info->sgsn_tlli.current == local_sgsn_tlli);
+	OSMO_ASSERT(link_info->sgsn_tlli.assigned == 0);
 
 	/* Detach */
 	send_llc_ul_ui(nsi, "DETACH REQ", &bss_peer[0], 0x1002,
diff --git a/openbsc/tests/gbproxy/gbproxy_test.ok b/openbsc/tests/gbproxy/gbproxy_test.ok
index 9ac1f4a..9dbcb45 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.ok
+++ b/openbsc/tests/gbproxy/gbproxy_test.ok
@@ -3084,7 +3084,7 @@
 
 NS UNITDATA MESSAGE to BSS, BVCI 0x1002, msg length 88 (gprs_ns_sendmsg)
 MESSAGE to BSS at 0x01020304:1111, msg length 92
-00 00 10 02 00 80 00 de ad 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 9e 41 c0 09 08 02 01 49 04 11 22 33 40 50 60 19 cd d7 08 17 16 18 05 f4 e6 56 aa 1f ab 9a 97 
+00 00 10 02 00 80 00 de ad 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 9e 41 c0 09 08 02 01 49 04 11 22 33 40 50 60 19 cd d7 08 17 16 18 05 f4 c0 0f 73 04 1e de 42 
 
 result (ATTACH ACCEPT (duplicated)) = 92
 
@@ -3098,7 +3098,7 @@
     Attach Request count            : 1
     TLLI cache size                 : 1
     TLLI-Cache: 1
-      TLLI 8000dead/e656aa1f -> 7c69fb81/efe2b700, IMSI 12131415161718, AGE 0
+      TLLI 8000dead/c00f7304 -> 7c69fb81/efe2b700, IMSI 12131415161718, AGE 0
 PROCESSING ATTACH COMPLETE from 0x01020304:1111
 00 00 10 02 01 c0 0f 73 04 00 00 04 08 88 11 22 33 40 50 60 12 34 00 80 0e 00 08 01 c0 09 08 03 39 d7 bc 
 
@@ -3107,7 +3107,7 @@
 
 NS UNITDATA MESSAGE to SGSN, BVCI 0x1002, msg length 31 (gprs_ns_sendmsg)
 MESSAGE to SGSN at 0x05060708:32000, msg length 35
-00 00 10 02 01 7e b5 2d fb 00 00 04 08 88 21 63 54 40 50 60 12 34 00 80 0e 00 08 01 c0 09 08 03 39 d7 bc 
+00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 21 63 54 40 50 60 12 34 00 80 0e 00 08 01 c0 09 08 03 39 d7 bc 
 
 result (ATTACH COMPLETE) = 35
 
@@ -3119,10 +3119,9 @@
     TLLI patched              (SGSN): 3
     P-TMSI patched            (SGSN): 2
     Attach Request count            : 1
-    TLLI cache size                 : 2
-    TLLI-Cache: 2
-      TLLI c00f7304 -> 7eb52dfb, IMSI (none), AGE 0
-      TLLI 8000dead/e656aa1f -> 7c69fb81/efe2b700, IMSI 12131415161718, AGE 0
+    TLLI cache size                 : 1
+    TLLI-Cache: 1
+      TLLI 8000dead/c00f7304 -> 7c69fb81/efe2b700, IMSI 12131415161718, AGE 0
 PROCESSING GMM INFO from 0x05060708:32000
 00 00 10 02 00 ef e2 b7 00 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 88 41 c0 0d 08 21 68 71 6b 
 
@@ -3131,7 +3130,7 @@
 
 NS UNITDATA MESSAGE to BSS, BVCI 0x1002, msg length 66 (gprs_ns_sendmsg)
 MESSAGE to BSS at 0x01020304:1111, msg length 70
-00 00 10 02 00 e6 56 aa 1f 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 88 41 c0 0d 08 21 68 71 6b 
+00 00 10 02 00 c0 0f 73 04 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 88 41 c0 0d 08 21 68 71 6b 
 
 result (GMM INFO) = 70
 
@@ -3143,10 +3142,9 @@
     TLLI patched              (SGSN): 4
     P-TMSI patched            (SGSN): 2
     Attach Request count            : 1
-    TLLI cache size                 : 2
-    TLLI-Cache: 2
-      TLLI 8000dead/e656aa1f -> 7c69fb81/efe2b700, IMSI 12131415161718, AGE 0
-      TLLI c00f7304 -> 7eb52dfb, IMSI (none), AGE 0
+    TLLI cache size                 : 1
+    TLLI-Cache: 1
+      TLLI c00f7304 -> efe2b700, IMSI 12131415161718, AGE 0
 PROCESSING DETACH REQ from 0x01020304:1111
 00 00 10 02 01 c0 0f 73 04 00 00 04 08 88 11 22 33 40 50 60 12 34 00 80 0e 00 15 01 c0 0d 08 05 01 18 05 f4 ef e2 b7 00 19 03 b9 97 cb 37 67 c6 
 
@@ -3155,7 +3153,7 @@
 
 NS UNITDATA MESSAGE to SGSN, BVCI 0x1002, msg length 44 (gprs_ns_sendmsg)
 MESSAGE to SGSN at 0x05060708:32000, msg length 48
-00 00 10 02 01 7e b5 2d fb 00 00 04 08 88 21 63 54 40 50 60 12 34 00 80 0e 00 15 01 c0 0d 08 05 01 18 05 f4 ef e2 b7 00 19 03 b9 97 cb 37 67 c6 
+00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 21 63 54 40 50 60 12 34 00 80 0e 00 15 01 c0 0d 08 05 01 18 05 f4 ef e2 b7 00 19 03 b9 97 cb 37 67 c6 
 
 result (DETACH REQ) = 48
 
@@ -3167,10 +3165,9 @@
     TLLI patched              (SGSN): 4
     P-TMSI patched            (SGSN): 2
     Attach Request count            : 1
-    TLLI cache size                 : 2
-    TLLI-Cache: 2
-      TLLI c00f7304 -> 7eb52dfb, IMSI (none), AGE 0
-      TLLI 8000dead/e656aa1f -> 7c69fb81/efe2b700, IMSI 12131415161718, AGE 0
+    TLLI cache size                 : 1
+    TLLI-Cache: 1
+      TLLI c00f7304 -> efe2b700, IMSI 12131415161718, AGE 0
 PROCESSING DETACH ACC from 0x05060708:32000
 00 00 10 02 00 ef e2 b7 00 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 89 41 c0 11 08 06 00 cf 8a 58 
 
@@ -3179,7 +3176,7 @@
 
 NS UNITDATA MESSAGE to BSS, BVCI 0x1002, msg length 67 (gprs_ns_sendmsg)
 MESSAGE to BSS at 0x01020304:1111, msg length 71
-00 00 10 02 00 e6 56 aa 1f 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 89 41 c0 11 08 06 00 cf 8a 58 
+00 00 10 02 00 c0 0f 73 04 00 50 20 16 82 02 58 13 99 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 0a 82 08 02 0d 88 11 12 13 14 15 16 17 18 00 81 00 0e 89 41 c0 11 08 06 00 cf 8a 58 
 
 result (DETACH ACC) = 71
 
@@ -3191,9 +3188,7 @@
     TLLI patched              (SGSN): 5
     P-TMSI patched            (SGSN): 2
     Attach Request count            : 1
-    TLLI cache size                 : 1
-    TLLI-Cache: 1
-      TLLI c00f7304 -> 7eb52dfb, IMSI (none), AGE 0
+    TLLI-Cache: 0
 Gbproxy global:
 === test_gbproxy_imsi_acquisition ===
 --- Initialise SGSN ---