diff --git a/api.planx.uk/send/exportZip.test.ts b/api.planx.uk/send/exportZip.test.ts
index 2ecb05da89..c402ebcc64 100644
--- a/api.planx.uk/send/exportZip.test.ts
+++ b/api.planx.uk/send/exportZip.test.ts
@@ -7,7 +7,6 @@ jest.mock("fs", () => ({
   existsSync: () => true,
   unlinkSync: () => undefined,
   createWriteStream: () => undefined,
-  writeFileSync: () => undefined,
   rmSync: () => undefined,
 }));
 
diff --git a/api.planx.uk/send/exportZip.ts b/api.planx.uk/send/exportZip.ts
index 80800d84e8..6c3dc6aac1 100644
--- a/api.planx.uk/send/exportZip.ts
+++ b/api.planx.uk/send/exportZip.ts
@@ -197,9 +197,7 @@ export class ExportZip {
       throw new Error("file not found");
     }
     const filePath = path.join(this.tmpDir, name);
-    fs.writeFileSync(filePath, body as Buffer);
-    this.zip.addLocalFile(filePath);
-    fs.unlinkSync(filePath);
+    this.zip.addFile(filePath, body as Buffer);
   }
 
   toBuffer(): Buffer {