diff --git a/src/libvlr/vlr_lu_fsm.c b/src/libvlr/vlr_lu_fsm.c
index 7500c86..5d8f78b 100644
--- a/src/libvlr/vlr_lu_fsm.c
+++ b/src/libvlr/vlr_lu_fsm.c
@@ -469,6 +469,8 @@
 		lu_compl_vlr_new_tmsi(fi);
 		return;
 	}
+	/* else, any previously used TMSI is now invalid. */
+	vsub->tmsi = GSM_RESERVED_TMSI;
 
 	/* Location Updating Accept */
 	vlr->ops.tx_lu_acc(lcvp->msc_conn_ref, GSM_RESERVED_TMSI);
@@ -514,6 +516,8 @@
 		/* Wait for TMSI ack */
 		return;
 	}
+	/* else, any previously used TMSI is now invalid. */
+	vsub->tmsi = GSM_RESERVED_TMSI;
 
 	/* No TMSI needed, accept now. */
 	vlr->ops.tx_lu_acc(lcvp->msc_conn_ref, GSM_RESERVED_TMSI);