diff --git a/CHANGES b/CHANGES
index 562164c945..5719cbd943 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+4829.	[bug]		isc_heap_delete did not zero the index value when
+			the heap was created with a callback to do that.
+			[RT #46709]
+
 4828.	[bug]		Do not use thread-local storage for storing LMDB reader
 			locktable slots. [RT #46556]
 
diff --git a/lib/isc/heap.c b/lib/isc/heap.c
index 6db7d0d25d..878bfed106 100644
--- a/lib/isc/heap.c
+++ b/lib/isc/heap.c
@@ -217,6 +217,8 @@ isc_heap_delete(isc_heap_t *heap, unsigned int idx) {
 	REQUIRE(idx >= 1 && idx <= heap->last);
 
 	heap_check(heap);
+	if (heap->index != NULL)
+		(heap->index)(heap->array[idx], 0);
 	if (idx == heap->last) {
 		heap->array[heap->last] = NULL;
 		heap->last--;
diff --git a/lib/isc/tests/Atffile b/lib/isc/tests/Atffile
index c22a19d66f..5ed35d264b 100644
--- a/lib/isc/tests/Atffile
+++ b/lib/isc/tests/Atffile
@@ -8,6 +8,7 @@ tp: counter_test
 tp: errno_test
 tp: file_test
 tp: hash_test
+tp: heap_test
 tp: ht_test
 tp: inet_ntop_test
 tp: lex_test
diff --git a/lib/isc/tests/Makefile.in b/lib/isc/tests/Makefile.in
index c2cd505422..7714d79747 100644
--- a/lib/isc/tests/Makefile.in
+++ b/lib/isc/tests/Makefile.in
@@ -26,21 +26,22 @@ LIBS =		@LIBS@ @ATFLIBS@
 
 OBJS =		isctest.@O@
 SRCS =		isctest.c aes_test.c buffer_test.c counter_test.c \
-		errno_test.c file_test.c hash_test.c ht_test.c \
-		inet_ntop_test.c lex_test.c mem_test.c netaddr_test.c \
-		parse_test.c pool_test.c print_test.c queue_test.c \
-		radix_test.c random_test.c regex_test.c result_test.c \
-		safe_test.c sockaddr_test.c socket_test.c socket_test.c \
-		symtab_test.c task_test.c taskpool_test.c time_test.c
+		errno_test.c file_test.c hash_test.c heap_test.c \
+		ht_test.c inet_ntop_test.c lex_test.c mem_test.c \
+		netaddr_test.c parse_test.c pool_test.c print_test.c \
+		queue_test.c radix_test.c random_test.c regex_test.c \
+		result_test.c safe_test.c sockaddr_test.c \
+		socket_test.c socket_test.c symtab_test.c task_test.c \
+		taskpool_test.c time_test.c
 
 SUBDIRS =
 TARGETS =	aes_test@EXEEXT@ buffer_test@EXEEXT@ counter_test@EXEEXT@ \
 		errno_test@EXEEXT@ file_test@EXEEXT@ hash_test@EXEEXT@ \
-		ht_test@EXEEXT@ inet_ntop_test@EXEEXT@ lex_test@EXEEXT@ \
-		mem_test@EXEEXT@ netaddr_test@EXEEXT@ parse_test@EXEEXT@ \
-		pool_test@EXEEXT@ print_test@EXEEXT@ queue_test@EXEEXT@ \
-		radix_test@EXEEXT@ random_test@EXEEXT@ regex_test@EXEEXT@ \
-		result_test@EXEEXT@ safe_test@EXEEXT@ \
+		heap_test@EXEEXT@ ht_test@EXEEXT@ inet_ntop_test@EXEEXT@ \
+		lex_test@EXEEXT@ mem_test@EXEEXT@ netaddr_test@EXEEXT@ \
+		parse_test@EXEEXT@ pool_test@EXEEXT@ print_test@EXEEXT@ \
+		queue_test@EXEEXT@ radix_test@EXEEXT@ random_test@EXEEXT@ \
+		regex_test@EXEEXT@ result_test@EXEEXT@ safe_test@EXEEXT@ \
 		sockaddr_test@EXEEXT@ socket_test@EXEEXT@ \
 		socket_test@EXEEXT@ symtab_test@EXEEXT@ task_test@EXEEXT@ \
 		taskpool_test@EXEEXT@ time_test@EXEEXT@
@@ -71,6 +72,10 @@ hash_test@EXEEXT@: hash_test.@O@ ${ISCDEPLIBS}
 	${LIBTOOL_MODE_LINK} ${PURIFY} ${CC} ${CFLAGS} ${LDFLAGS} -o $@ \
 			hash_test.@O@ ${ISCLIBS} ${LIBS}
 
+heap_test@EXEEXT@: heap_test.@O@ ${ISCDEPLIBS}
+	${LIBTOOL_MODE_LINK} ${PURIFY} ${CC} ${CFLAGS} ${LDFLAGS} -o $@ \
+			heap_test.@O@ ${ISCLIBS} ${LIBS}
+
 ht_test@EXEEXT@: ht_test.@O@ ${ISCDEPLIBS}
 	${LIBTOOL_MODE_LINK} ${PURIFY} ${CC} ${CFLAGS} ${LDFLAGS} -o $@ \
 			ht_test.@O@ ${ISCLIBS} ${LIBS}
diff --git a/lib/isc/tests/heap_test.c b/lib/isc/tests/heap_test.c
new file mode 100644
index 0000000000..03c08e34be
--- /dev/null
+++ b/lib/isc/tests/heap_test.c
@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2011-2017  Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/* ! \file */
+
+#include <config.h>
+
+#include <atf-c.h>
+
+#include <stdio.h>
+#include <string.h>
+
+#include <isc/heap.h>
+#include <isc/mem.h>
+
+#include <isc/util.h>
+
+struct e {
+	unsigned int value;
+	unsigned int index;
+};
+
+static isc_boolean_t
+compare(void *p1, void *p2) {
+	struct e *e1 = p1;
+	struct e *e2 = p2;
+
+	return (ISC_TF(e1->value < e2->value));
+}
+
+static void
+idx(void *p, unsigned int i) {
+	struct e *e = p;
+
+	e->index = i;
+}
+
+ATF_TC(isc_heap_delete);
+ATF_TC_HEAD(isc_heap_delete, tc) {
+	atf_tc_set_md_var(tc, "descr", "test isc_heap_delete");
+}
+ATF_TC_BODY(isc_heap_delete, tc) {
+	isc_mem_t *mctx = NULL;
+	isc_heap_t *heap = NULL;
+	isc_result_t result;
+	struct e e1 = { 100, 0 };
+
+	UNUSED(tc);
+
+	result = isc_mem_create(0, 0, &mctx);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+
+	result = isc_heap_create(mctx, compare, idx, 0, &heap);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+	ATF_REQUIRE(heap != NULL);
+
+	isc_heap_insert(heap, &e1);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+	ATF_REQUIRE_EQ(e1.index, 1);
+
+	isc_heap_delete(heap, e1.index);
+	ATF_CHECK_EQ(e1.index, 0);
+
+	isc_heap_destroy(&heap);
+	ATF_REQUIRE_EQ(heap, NULL);
+
+	isc_mem_detach(&mctx);
+	ATF_REQUIRE_EQ(mctx, NULL);
+}
+
+/*
+ * Main
+ */
+ATF_TP_ADD_TCS(tp) {
+	ATF_TP_ADD_TC(tp, isc_heap_delete);
+
+	return (atf_no_error());
+}