diff --git a/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/include/img_mgmt/img_mgmt.h b/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/include/img_mgmt/img_mgmt.h
index 9861199c251..32c73b26a7e 100644
--- a/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/include/img_mgmt/img_mgmt.h
+++ b/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/include/img_mgmt/img_mgmt.h
@@ -41,6 +41,7 @@ extern "C" {
 #define IMG_MGMT_SWAP_TYPE_TEST		1
 #define IMG_MGMT_SWAP_TYPE_PERM		2
 #define IMG_MGMT_SWAP_TYPE_REVERT	3
+#define IMG_MGMT_SWAP_TYPE_UNKNOWN	255
 
 /**
  * Command IDs for image management group.
diff --git a/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/src/zephyr_img_mgmt.c b/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/src/zephyr_img_mgmt.c
index 80c3c4973c0..3d39a357426 100644
--- a/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/src/zephyr_img_mgmt.c
+++ b/subsys/mgmt/mcumgr/lib/cmd/img_mgmt/src/zephyr_img_mgmt.c
@@ -511,8 +511,7 @@ img_mgmt_impl_swap_type(int slot)
 	case BOOT_SWAP_TYPE_REVERT:
 		return IMG_MGMT_SWAP_TYPE_REVERT;
 	default:
-		assert(0);
-		return IMG_MGMT_SWAP_TYPE_NONE;
+		return IMG_MGMT_SWAP_TYPE_UNKNOWN;
 	}
 }