diff --git a/CHANGES b/CHANGES
index 4b93b761a0..d09f3a9478 100644
--- a/CHANGES
+++ b/CHANGES
@@ -28,7 +28,10 @@
 5245.	[cleanup]	Reduce logging level for IXFR up-to-date poll
 			responses. [GL #1009]
 
-5244.	[placeholder]
+5244.	[security]	Fixed a race condition in dns_dispatch_getnext()
+			that could cause an assertion failure if a
+			significant number of incoming packets were
+			rejected. (CVE-2019-6471) [GL #942]
 
 5243.	[bug]		Fix a possible race between dispatcher and socket
 			code in a high-load cold-cache resolver scenario.
diff --git a/doc/arm/notes.xml b/doc/arm/notes.xml
index 8d09e12986..6d897437ba 100644
--- a/doc/arm/notes.xml
+++ b/doc/arm/notes.xml
@@ -97,7 +97,15 @@
 	<para>
 	  The TCP client quota set using the <command>tcp-clients</command>
 	  option could be exceeded in some cases. This could lead to
-	  exhaustion of file descriptors. (CVE-2018-5743) [GL #615]
+	  exhaustion of file descriptors. This flaw is disclosed in
+	  CVE-2018-5743. [GL #615]
+	</para>
+      </listitem>
+      <listitem>
+	<para>
+	  A race condition could trigger an assertion failure when
+	  a large number of incoming packets were being rejected.
+	  This flaw is disclosed in CVE-2019-6471. [GL #942]
 	</para>
       </listitem>
     </itemizedlist>
diff --git a/lib/dns/dispatch.c b/lib/dns/dispatch.c
index 2b37d29097..a5dd6d75b4 100644
--- a/lib/dns/dispatch.c
+++ b/lib/dns/dispatch.c
@@ -126,7 +126,7 @@ struct dns_dispentry {
 	isc_task_t		       *task;
 	isc_taskaction_t		action;
 	void			       *arg;
-	bool			item_out;
+	bool				item_out;
 	dispsocket_t			*dispsocket;
 	ISC_LIST(dns_dispatchevent_t)	items;
 	ISC_LINK(dns_dispentry_t)	link;
@@ -3271,13 +3271,14 @@ dns_dispatch_getnext(dns_dispentry_t *resp, dns_dispatchevent_t **sockevent) {
 	disp = resp->disp;
 	REQUIRE(VALID_DISPATCH(disp));
 
-	REQUIRE(resp->item_out == true);
-	resp->item_out = false;
-
 	ev = *sockevent;
 	*sockevent = NULL;
 
 	LOCK(&disp->lock);
+
+	REQUIRE(resp->item_out == true);
+	resp->item_out = false;
+
 	if (ev->buffer.base != NULL)
 		free_buffer(disp, ev->buffer.base, ev->buffer.length);
 	free_devent(disp, ev);
@@ -3422,6 +3423,9 @@ dns_dispatch_removeresponse(dns_dispentry_t **resp,
 		isc_task_send(disp->task[0], &disp->ctlevent);
 }
 
+/*
+ * disp must be locked.
+ */
 static void
 do_cancel(dns_dispatch_t *disp) {
 	dns_dispatchevent_t *ev;