diff --git a/RELNOTES b/RELNOTES
index a7027019..b6daddf9 100644
--- a/RELNOTES
+++ b/RELNOTES
@@ -54,6 +54,11 @@ by Eric Young (eay@cryptsoft.com).
 
 			Changes since 4.3.2
 
+- Delayed-ack now works properly with Failover. Prior to this, bind updates
+  post startup were being queued but never delivered. Among other things, this
+  was causing leases to not transition from expired or released to free.
+  [ISC-Bugs #31474]
+
 - The server now does a better check to see if it can allocate the memory
   for large blocks of v4 leases and should provide a slightly better error
   message.  Note well: the server pre-allocates v4 addresses, if you use
diff --git a/includes/dhcpd.h b/includes/dhcpd.h
index 2a43229f..378459b9 100644
--- a/includes/dhcpd.h
+++ b/includes/dhcpd.h
@@ -2313,9 +2313,7 @@ void ack_lease (struct packet *, struct lease *,
 		unsigned int, TIME, char *, int, struct host_decl *);
 void echo_client_id(struct packet*, struct lease*, struct option_state*,
 		    struct option_state*);
-void delayed_ack_enqueue(struct lease *);
-void commit_leases_readerdry(void *);
-void flush_ackqueue(void *);
+
 void dhcp_reply (struct lease *);
 int find_lease (struct lease **, struct packet *,
 		struct shared_network *, int *, int *, struct lease *,
@@ -2953,7 +2951,6 @@ isc_result_t write_named_billing_class(const void *, unsigned, void *);
 void write_billing_classes (void);
 int write_billing_class (struct class *);
 void commit_leases_timeout (void *);
-void commit_leases_readerdry(void *);
 int commit_leases (void);
 int commit_leases_timed (void);
 void db_startup (int);
diff --git a/server/db.c b/server/db.c
index e1f1beb7..d4d42feb 100644
--- a/server/db.c
+++ b/server/db.c
@@ -3,7 +3,7 @@
    Persistent database management routines for DHCPD... */
 
 /*
- * Copyright (c) 2012-2014 by Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (c) 2012-2015 by Internet Systems Consortium, Inc. ("ISC")
  * Copyright (c) 2004-2010 by Internet Systems Consortium, Inc. ("ISC")
  * Copyright (c) 1995-2003 by Internet Software Consortium
  *
@@ -1017,9 +1017,6 @@ int commit_leases ()
 		return (0);
 	}
 
-	/* send out all deferred ACKs now */
-	flush_ackqueue(NULL);
-
 	/* If we haven't rewritten the lease database in over an
 	   hour, rewrite it now.  (The length of time should probably
 	   be configurable. */
diff --git a/server/dhcp.c b/server/dhcp.c
index e71720f6..ba32c5b4 100644
--- a/server/dhcp.c
+++ b/server/dhcp.c
@@ -31,7 +31,6 @@
 #include <limits.h>
 #include <sys/time.h>
 
-static void commit_leases_ackout(void *foo);
 static void maybe_return_agent_options(struct packet *packet,
 				       struct option_state *options);
 static int reuse_lease (struct packet* packet, struct lease* new_lease,
@@ -40,6 +39,11 @@ static int reuse_lease (struct packet* packet, struct lease* new_lease,
 
 int outstanding_pings;
 
+#if defined(DELAYED_ACK)
+static void delayed_ack_enqueue(struct lease *);
+static void delayed_acks_timer(void *);
+
+
 struct leasequeue *ackqueue_head, *ackqueue_tail;
 static struct leasequeue *free_ackqueue;
 static struct timeval max_fsync;
@@ -49,6 +53,7 @@ int max_outstanding_acks = DEFAULT_DELAYED_ACK;
 int max_ack_delay_secs = DEFAULT_ACK_DELAY_SECS;
 int max_ack_delay_usecs = DEFAULT_ACK_DELAY_USECS;
 int min_ack_delay_usecs = DEFAULT_MIN_ACK_DELAY_USECS;
+#endif
 
 static char dhcp_message [256];
 static int site_code_min;
@@ -3368,6 +3373,8 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
 	}
 }
 
+#if defined(DELAYED_ACK)
+
 /*
  * CC: queue single ACK:
  * - write the lease (but do not fsync it yet)
@@ -3377,7 +3384,7 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
  *   but only up to the max timer value.
  */
 
-void
+static void
 delayed_ack_enqueue(struct lease *lease)
 {
 	struct leasequeue *q;
@@ -3405,11 +3412,9 @@ delayed_ack_enqueue(struct lease *lease)
 
 	outstanding_acks++;
 	if (outstanding_acks > max_outstanding_acks) {
-		commit_leases();
-
-		/* Reset max_fsync and cancel any pending timeout. */
-		memset(&max_fsync, 0, sizeof(max_fsync));
-		cancel_timeout(commit_leases_ackout, NULL);
+		/* Cancel any pending timeout and call handler directly */
+		cancel_timeout(delayed_acks_timer, NULL);
+		delayed_acks_timer(NULL);
 	} else {
 		struct timeval next_fsync;
 
@@ -3440,44 +3445,68 @@ delayed_ack_enqueue(struct lease *lease)
 			next_fsync.tv_usec = max_fsync.tv_usec;
 		}
 
-		add_timeout(&next_fsync, commit_leases_ackout, NULL,
+		add_timeout(&next_fsync, delayed_acks_timer, NULL,
 			    (tvref_t) NULL, (tvunref_t) NULL);
 	}
 }
 
-static void
-commit_leases_ackout(void *foo)
-{
-	if (outstanding_acks) {
-		commit_leases();
-
-		memset(&max_fsync, 0, sizeof(max_fsync));
-	}
-}
-
-/* CC: process the delayed ACK responses:
-   - send out the ACK packets
-   - move the queue slots to the free list
+/* Processes any delayed acks:
+ * Commits the leases and then for each delayed ack:
+ *  - Update the failover peer if we're in failover
+ *  - Send the REPLY to the client
  */
-void
-flush_ackqueue(void *foo) 
+static void
+delayed_acks_timer(void *foo)
 {
 	struct leasequeue *ack, *p;
+
+	/* Reset max fsync */
+	memset(&max_fsync, 0, sizeof(max_fsync));
+
+	if (!outstanding_acks) {
+		/* Nothing to do, so punt, shouldn't happen? */
+		return;
+	}
+
+	/* Commit the leases first */
+	commit_leases();
+
+	/* Now process the delayed ACKs
+	 - update failover peer
+	 - send out the ACK packets
+	 - move the queue slots to the free list
+	*/
+
 	/*  process from bottom to retain packet order */
 	for (ack = ackqueue_tail ; ack ; ack = p) { 
 		p = ack->prev;
 
+#if defined(FAILOVER_PROTOCOL)
+		/* If we're in failover we need to send any deferred
+		* bind updates as well as the replies */
+		if (ack->lease->pool) {
+			dhcp_failover_state_t *fpeer;
+
+			fpeer = ack->lease->pool->failover_peer;
+			if (fpeer && fpeer->link_to_peer) {
+				dhcp_failover_send_updates(fpeer);
+			}
+		}
+#endif
+
 		/* dhcp_reply() requires that the reply state still be valid */
 		if (ack->lease->state == NULL)
 			log_error("delayed ack for %s has gone stale",
 				  piaddr(ack->lease->ip_addr));
-		else
+		else {
 			dhcp_reply(ack->lease);
+		}
 
 		lease_dereference(&ack->lease, MDL);
 		ack->next = free_ackqueue;
 		free_ackqueue = ack;
 	}
+
 	ackqueue_head = NULL;
 	ackqueue_tail = NULL;
 	outstanding_acks = 0;
@@ -3500,6 +3529,8 @@ relinquish_ackqueue(void)
 }
 #endif
 
+#endif /* defined(DELAYED_ACK) */
+
 void dhcp_reply (lease)
 	struct lease *lease;
 {
diff --git a/server/dhcpd.c b/server/dhcpd.c
index cb4f0112..ebb6d3e3 100644
--- a/server/dhcpd.c
+++ b/server/dhcpd.c
@@ -1059,7 +1059,8 @@ void postconf_initialization (int quiet)
 			data_string_forget(&db, MDL);
 		}
 	}
-	
+
+#if defined(DELAYED_ACK)
 	oc = lookup_option(&server_universe, options, SV_DELAYED_ACK);
 	if (oc &&
 	    evaluate_option_cache(&db, NULL, NULL, NULL, options, NULL,
@@ -1087,6 +1088,7 @@ void postconf_initialization (int quiet)
 
 		data_string_forget(&db, MDL);
 	}
+#endif
 
 	oc = lookup_option(&server_universe, options, SV_DONT_USE_FSYNC);
 	if ((oc != NULL) &&