diff --git a/app/api/projects/[projectId]/videos/[videoId]/versions/route.ts b/app/api/projects/[projectId]/videos/[videoId]/versions/route.ts
index 44d60ea..2ab73ea 100644
--- a/app/api/projects/[projectId]/videos/[videoId]/versions/route.ts
+++ b/app/api/projects/[projectId]/videos/[videoId]/versions/route.ts
@@ -2,7 +2,6 @@ import { NextRequest } from 'next/server';
 import { db } from '@/lib/db';
 import { auth, checkProjectAccess } from '@/lib/auth';
 import { validateUrl, validateOptionalUrlOrAppPath } from '@/lib/validation';
-import { toJsonSafe } from '@/lib/json-serialize';
 import { rateLimit } from '@/lib/rate-limit';
 import { notifyProjectOwner } from '@/lib/notifications';
 import { apiErrors, successResponse, withCacheControl } from '@/lib/api-response';
@@ -264,7 +263,7 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
       }).catch((err) => logError('Notification failed:', err));
     }
 
-    const response = successResponse(toJsonSafe(version), 201);
+    const response = successResponse(version, 201);
     return withCacheControl(response, 'private, no-store');
   } catch (error) {
     logError('Error creating version:', error);
diff --git a/app/api/projects/[projectId]/videos/route.ts b/app/api/projects/[projectId]/videos/route.ts
index 66d9838..86ce0fa 100644
--- a/app/api/projects/[projectId]/videos/route.ts
+++ b/app/api/projects/[projectId]/videos/route.ts
@@ -2,7 +2,6 @@ import { NextRequest } from 'next/server';
 import { db } from '@/lib/db';
 import { auth, checkProjectAccess } from '@/lib/auth';
 import { validateUrl, validateOptionalUrlOrAppPath } from '@/lib/validation';
-import { toJsonSafe } from '@/lib/json-serialize';
 import { rateLimit } from '@/lib/rate-limit';
 import { notifyProjectOwner } from '@/lib/notifications';
 import { apiErrors, successResponse, withCacheControl } from '@/lib/api-response';
@@ -269,7 +268,7 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
       }).catch((err) => logError('Notification failed:', err));
     }
 
-    const response = successResponse(toJsonSafe(video), 201);
+    const response = successResponse(video, 201);
     return withCacheControl(response, 'private, no-store');
   } catch (error) {
     logError('Error creating video:', error);
diff --git a/lib/api-response.ts b/lib/api-response.ts
index 5a59d50..6afa021 100644
--- a/lib/api-response.ts
+++ b/lib/api-response.ts
@@ -1,4 +1,5 @@
 import { NextResponse } from 'next/server';
+import { bigIntReplacer } from '@/lib/json-serialize';
 
 /**
  * Standardized API error response format
@@ -113,6 +114,11 @@ export function errorResponse(
  * @param status - HTTP status code (default: 200)
  * @param meta - Pagination or other metadata (optional)
  *
+ * Serialized with bigIntReplacer rather than NextResponse.json(), because
+ * JSON.stringify throws on BigInt and Prisma returns BigInt for sizeBytes.
+ * Any payload carrying a VideoVersion or VideoAsset row would otherwise 500
+ * after its write had already committed. BigInt values render as strings.
+ *
  * @example
  * ```ts
  * return successResponse({ projects: [] });
@@ -127,7 +133,10 @@ export function successResponse<T>(
   const body: ApiSuccessResponse<T> = { data };
   if (meta) body.meta = meta;
 
-  return NextResponse.json(body, { status });
+  return new NextResponse(JSON.stringify(body, bigIntReplacer), {
+    status,
+    headers: { 'content-type': 'application/json' },
+  }) as NextResponse<ApiSuccessResponse<T>>;
 }
 
 export function withCacheControl(response: Response, value: string): Response {
diff --git a/lib/json-serialize.ts b/lib/json-serialize.ts
index 39cc85a..9343256 100644
--- a/lib/json-serialize.ts
+++ b/lib/json-serialize.ts
@@ -1,8 +1,18 @@
+/**
+ * JSON.stringify replacer that renders Prisma BigInt columns (sizeBytes) as
+ * strings. Without it, JSON.stringify throws on any payload carrying one.
+ */
+export function bigIntReplacer(_key: string, value: unknown): unknown {
+  return typeof value === 'bigint' ? value.toString() : value;
+}
+
 /**
  * Converts values for JSON responses (e.g. Prisma BigInt fields).
+ *
+ * API routes do not need this — successResponse() serializes BigInt already.
+ * Use it for payloads that bypass that helper, such as data handed from a
+ * server component to a client component.
  */
 export function toJsonSafe<T>(value: T): T {
-  return JSON.parse(
-    JSON.stringify(value, (_key, val) => (typeof val === 'bigint' ? val.toString() : val))
-  ) as T;
+  return JSON.parse(JSON.stringify(value, bigIntReplacer)) as T;
 }