diff --git a/bin/dig/dig.c b/bin/dig/dig.c
index d4867cc282..3e59f7f21a 100644
--- a/bin/dig/dig.c
+++ b/bin/dig/dig.c
@@ -3079,7 +3079,7 @@ void
 dig_shutdown(void) {
 	destroy_lookup(default_lookup);
 	if (atomic_load(&batchname) != 0) {
-		if (batchfp != stdin) {
+		if (batchfp != NULL && batchfp != stdin) {
 			fclose(batchfp);
 		}
 		atomic_store(&batchname, 0);
diff --git a/lib/isc/netmgr/tcp.c b/lib/isc/netmgr/tcp.c
index 37d44bd9c8..7c77b6cb74 100644
--- a/lib/isc/netmgr/tcp.c
+++ b/lib/isc/netmgr/tcp.c
@@ -424,9 +424,10 @@ start_tcp_child(isc_nm_t *mgr, isc_sockaddr_t *iface, isc_nmsocket_t *sock,
 		csock->fd = isc__nm_tcp_lb_socket(mgr,
 						  iface->type.sa.sa_family);
 	} else {
+		INSIST(fd >= 0);
 		csock->fd = dup(fd);
 	}
-	REQUIRE(csock->fd >= 0);
+	INSIST(csock->fd >= 0);
 
 	ievent = isc__nm_get_netievent_tcplisten(mgr, csock);
 	isc__nm_maybe_enqueue_ievent(&mgr->workers[tid],
diff --git a/lib/isc/netmgr/tcpdns.c b/lib/isc/netmgr/tcpdns.c
index 4b5ee58b6a..6ce4a61e68 100644
--- a/lib/isc/netmgr/tcpdns.c
+++ b/lib/isc/netmgr/tcpdns.c
@@ -397,9 +397,10 @@ start_tcpdns_child(isc_nm_t *mgr, isc_sockaddr_t *iface, isc_nmsocket_t *sock,
 		csock->fd = isc__nm_tcpdns_lb_socket(mgr,
 						     iface->type.sa.sa_family);
 	} else {
+		INSIST(fd >= 0);
 		csock->fd = dup(fd);
 	}
-	REQUIRE(csock->fd >= 0);
+	INSIST(csock->fd >= 0);
 
 	ievent = isc__nm_get_netievent_tcpdnslisten(mgr, csock);
 	isc__nm_maybe_enqueue_ievent(&mgr->workers[tid],
diff --git a/lib/isc/netmgr/tlsdns.c b/lib/isc/netmgr/tlsdns.c
index dcec05347f..b56e0682b1 100644
--- a/lib/isc/netmgr/tlsdns.c
+++ b/lib/isc/netmgr/tlsdns.c
@@ -501,9 +501,10 @@ start_tlsdns_child(isc_nm_t *mgr, isc_sockaddr_t *iface, isc_nmsocket_t *sock,
 		csock->fd = isc__nm_tlsdns_lb_socket(mgr,
 						     iface->type.sa.sa_family);
 	} else {
+		INSIST(fd >= 0);
 		csock->fd = dup(fd);
 	}
-	REQUIRE(csock->fd >= 0);
+	INSIST(csock->fd >= 0);
 
 	ievent = isc__nm_get_netievent_tlsdnslisten(mgr, csock);
 	isc__nm_maybe_enqueue_ievent(&mgr->workers[tid],
diff --git a/lib/isc/netmgr/udp.c b/lib/isc/netmgr/udp.c
index 661de96ac6..1956a185ef 100644
--- a/lib/isc/netmgr/udp.c
+++ b/lib/isc/netmgr/udp.c
@@ -129,9 +129,10 @@ start_udp_child(isc_nm_t *mgr, isc_sockaddr_t *iface, isc_nmsocket_t *sock,
 		csock->fd = isc__nm_udp_lb_socket(mgr,
 						  iface->type.sa.sa_family);
 	} else {
+		INSIST(fd >= 0);
 		csock->fd = dup(fd);
 	}
-	REQUIRE(csock->fd >= 0);
+	INSIST(csock->fd >= 0);
 
 	ievent = isc__nm_get_netievent_udplisten(mgr, csock);
 	isc__nm_maybe_enqueue_ievent(&mgr->workers[tid],