diff --git a/pri.c b/pri.c
index d5ac4c5..5ff84fd 100644
--- a/pri.c
+++ b/pri.c
@@ -1646,11 +1646,43 @@ int pri_set_crv(struct pri *pri, q931_call *call, int crv, int callmode)
 
 void pri_enslave(struct pri *master, struct pri *slave)
 {
-	if (master && slave) {
-		slave->callpool = &master->localpool;
-		slave->nfas = 1;
-		master->nfas = 1;
+	if (!master || !slave) {
+		return;
 	}
+
+	if (slave->master) {
+		struct pri *swp;
+
+		/* The slave already has a master */
+		if (master->master || master->slave) {
+			/* The new master has a master or it already has slaves. */
+			return;
+		}
+
+		/* Swap master and slave. */
+		swp = master;
+		master = slave;
+		slave = master;
+	}
+
+	/*
+	 * To have some support for dynamic interfaces, the master NFAS
+	 * D channel control structure will always exist even if it is
+	 * abandoned/deleted by the upper layer.  The master/slave
+	 * pointers ensure that the correct master will be used.
+	 */
+
+	master = PRI_NFAS_MASTER(master);
+	master->nfas = 1;
+	slave->nfas = 1;
+	slave->callpool = &master->localpool;
+
+	/* Link the slave to the master on the end of the master's list. */
+	slave->master = master;
+	slave->slave = NULL;
+	for (; master->slave; master = master->slave) {
+	}
+	master->slave = slave;
 }
 
 struct pri_sr *pri_sr_new(void)
diff --git a/pri_internal.h b/pri_internal.h
index 74abc58..8235092 100644
--- a/pri_internal.h
+++ b/pri_internal.h
@@ -76,6 +76,10 @@ struct pri {
 	void *userdata;
 	/*! Accumulated pri_message() line. (Valid in master record only) */
 	struct pri_msg_line *msg_line;
+	/*! NFAS master/primary channel if appropriate */
+	struct pri *master;
+	/*! Next NFAS slaved D channel if appropriate */
+	struct pri *slave;
 	struct {
 		/*! Dynamically allocated array of timers that can grow as needed. */
 		struct pri_sched *timer;
@@ -951,6 +955,21 @@ int pri_cc_event(struct pri *ctrl, q931_call *call, struct pri_cc_record *cc_rec
 int q931_cc_timeout(struct pri *ctrl, struct pri_cc_record *cc_record, enum CC_EVENTS event);
 void q931_cc_indirect(struct pri *ctrl, struct pri_cc_record *cc_record, void (*func)(struct pri *ctrl, q931_call *call, struct pri_cc_record *cc_record));
 
+/*!
+ * \brief Get the NFAS master PRI control structure.
+ *
+ * \param ctrl D channel controller.
+ *
+ * \return NFAS master PRI control structure.
+ */
+static inline struct pri *PRI_NFAS_MASTER(struct pri *ctrl)
+{
+	while (ctrl->master) {
+		ctrl = ctrl->master;
+	}
+	return ctrl;
+}
+
 /*!
  * \brief Determine if layer 2 is in BRI NT PTMP mode.
  *