diff --git a/src/apps/cli/services/NodeKeyValueDBService.ts b/src/apps/cli/services/NodeKeyValueDBService.ts
index 421fa0f5..c39372da 100644
--- a/src/apps/cli/services/NodeKeyValueDBService.ts
+++ b/src/apps/cli/services/NodeKeyValueDBService.ts
@@ -25,6 +25,10 @@ type SerializableContainer =
     | {
           [NODE_KV_TYPED_KEY]: "ArrayBuffer";
           [NODE_KV_VALUES_KEY]: number[];
+      }
+    | {
+          [NODE_KV_TYPED_KEY]: "BigInt";
+          [NODE_KV_VALUES_KEY]: string;
       };
 
 function isRecord(value: unknown): value is Record<string, unknown> {
@@ -32,6 +36,12 @@ function isRecord(value: unknown): value is Record<string, unknown> {
 }
 
 function serializeForNodeKV(value: unknown): unknown {
+    if (typeof value === "bigint") {
+        return {
+            [NODE_KV_TYPED_KEY]: "BigInt",
+            [NODE_KV_VALUES_KEY]: value.toString(10),
+        } satisfies SerializableContainer;
+    }
     if (value instanceof Set) {
         return {
             [NODE_KV_TYPED_KEY]: "Set",
@@ -78,6 +88,9 @@ function deserializeFromNodeKV(value: unknown): unknown {
     if (taggedType === "ArrayBuffer" && Array.isArray(taggedValues)) {
         return Uint8Array.from(taggedValues).buffer;
     }
+    if (taggedType === "BigInt" && typeof taggedValues === "string" && /^-?(?:0|[1-9]\d*)$/u.test(taggedValues)) {
+        return BigInt(taggedValues);
+    }
 
     return Object.fromEntries(Object.entries(value).map(([k, v]) => [k, deserializeFromNodeKV(v)]));
 }
diff --git a/src/apps/cli/services/NodeKeyValueDBService.unit.spec.ts b/src/apps/cli/services/NodeKeyValueDBService.unit.spec.ts
index a8d3d1d4..f362b781 100644
--- a/src/apps/cli/services/NodeKeyValueDBService.unit.spec.ts
+++ b/src/apps/cli/services/NodeKeyValueDBService.unit.spec.ts
@@ -1,8 +1,39 @@
 import { describe, expect, it, vi } from "vitest";
 import { createServiceContext } from "@vrtmrz/livesync-commonlib/compat/services/base/ServiceBase";
+import { fsPromises as fs, os, path } from "@vrtmrz/livesync-commonlib/node";
 import type { NodeKeyValueDBDependencies } from "./NodeKeyValueDBService";
 import { NodeKeyValueDBService } from "./NodeKeyValueDBService";
 
+function createInitialisableDependencies(): {
+    dependencies: NodeKeyValueDBDependencies;
+    initialise: () => Promise<boolean>;
+} {
+    let initialise: (() => Promise<boolean>) | undefined;
+    const dependencies = {
+        appLifecycle: {
+            onSettingLoaded: {
+                addHandler: vi.fn((handler: () => Promise<boolean>) => {
+                    initialise = handler;
+                }),
+            },
+        },
+        databaseEvents: {
+            onResetDatabase: { addHandler: vi.fn() },
+            onDatabaseInitialisation: { addHandler: vi.fn() },
+            onUnloadDatabase: { addHandler: vi.fn() },
+            onCloseDatabase: { addHandler: vi.fn() },
+        },
+        vault: {},
+    } as unknown as NodeKeyValueDBDependencies;
+    return {
+        dependencies,
+        initialise: async () => {
+            if (!initialise) throw new Error("Initialisation handler was not registered");
+            return await initialise();
+        },
+    };
+}
+
 describe("NodeKeyValueDBService.openSimpleStore", () => {
     it("creates a namespaced store handle before the backing database is initialised", () => {
         const dependencies = {
@@ -44,4 +75,28 @@ describe("NodeKeyValueDBService.openSimpleStore", () => {
 
         await expect(store.get("key")).rejects.toThrow("KeyValueDB is not initialized yet");
     });
+
+    it("preserves bigint values used by Adaptive Journal writer state", async () => {
+        const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "livesync-node-kv-bigint-"));
+        const filePath = path.join(tempDir, "keyvalue-db.json");
+        const writerState = {
+            writerEpoch: 9007199254740993n,
+            nested: [0n, { sequence: 18446744073709551615n }],
+        };
+
+        try {
+            const firstLifecycle = createInitialisableDependencies();
+            const first = new NodeKeyValueDBService(createServiceContext(), firstLifecycle.dependencies, filePath);
+            await expect(firstLifecycle.initialise()).resolves.toBe(true);
+            await first.openSimpleStore("adaptive").set("writer-state", writerState);
+
+            const secondLifecycle = createInitialisableDependencies();
+            const second = new NodeKeyValueDBService(createServiceContext(), secondLifecycle.dependencies, filePath);
+            await expect(secondLifecycle.initialise()).resolves.toBe(true);
+
+            await expect(second.openSimpleStore("adaptive").get("writer-state")).resolves.toEqual(writerState);
+        } finally {
+            await fs.rm(tempDir, { recursive: true, force: true });
+        }
+    });
 });