diff --git a/subsys/mgmt/mcumgr/bootutil_hooks/nrf53_hooks.c b/subsys/mgmt/mcumgr/bootutil_hooks/nrf53_hooks.c
index 9971a4e0843..f1ac8a168e6 100644
--- a/subsys/mgmt/mcumgr/bootutil_hooks/nrf53_hooks.c
+++ b/subsys/mgmt/mcumgr/bootutil_hooks/nrf53_hooks.c
@@ -8,10 +8,18 @@
 #include <zephyr/device.h>
 #include "bootutil/bootutil_public.h"
 
+#if CONFIG_MCUBOOT_NETWORK_CORE_IMAGE_NUMBER != -1
+/* Sysbuild */
+#define NET_CORE_IMAGE CONFIG_MCUBOOT_NETWORK_CORE_IMAGE_NUMBER
+#else
+/* Legacy child/parent */
+#define NET_CORE_IMAGE 1
+#endif
+
 int boot_read_swap_state_primary_slot_hook(int image_index,
 		struct boot_swap_state *state)
 {
-	if (image_index == 1) {
+	if (image_index == NET_CORE_IMAGE) {
 		/* Pretend that primary slot of image 1 unpopulated */
 		state->magic = BOOT_MAGIC_UNSET;
 		state->swap_type = BOOT_SWAP_TYPE_NONE;