diff --git a/client/src/components/Planner/BookingImportModal.test.tsx b/client/src/components/Planner/BookingImportModal.test.tsx
index ea5cdcdb9..54063390e 100644
--- a/client/src/components/Planner/BookingImportModal.test.tsx
+++ b/client/src/components/Planner/BookingImportModal.test.tsx
@@ -3,6 +3,7 @@ import { render, screen, fireEvent, waitFor } from '../../../tests/helpers/rende
 import userEvent from '@testing-library/user-event';
 import { http, HttpResponse } from 'msw';
 import { server } from '../../../tests/helpers/msw/server';
+import { readMultipart } from '../../../tests/helpers/multipart';
 import { useBackgroundTasksStore } from '../../store/backgroundTasksStore';
 import { resetAllStores } from '../../../tests/helpers/store';
 import { saveImportFiles } from '../../db/offlineDb';
@@ -111,8 +112,7 @@ describe('BookingImportModal', () => {
     let sentMode: string | null = null;
     server.use(
       http.post('/api/trips/4/reservations/import/booking/async', async ({ request }) => {
-        const fd = await request.formData();
-        sentMode = String(fd.get('mode'));
+        sentMode = (await readMultipart(request)).fields.mode ?? null;
         return HttpResponse.json({ jobId: 'job-42' });
       }),
     );
@@ -132,8 +132,7 @@ describe('BookingImportModal', () => {
     server.use(
       http.get('/api/health/features', () => HttpResponse.json({ bookingImport: true, aiParsing: true })),
       http.post('/api/trips/4/reservations/import/booking/async', async ({ request }) => {
-        const fd = await request.formData();
-        sentMode = String(fd.get('mode'));
+        sentMode = (await readMultipart(request)).fields.mode ?? null;
         return HttpResponse.json({ jobId: 'job-ai' });
       }),
     );
diff --git a/client/src/components/Planner/FileImportModal.test.tsx b/client/src/components/Planner/FileImportModal.test.tsx
index fe4ee533f..fcd540760 100644
--- a/client/src/components/Planner/FileImportModal.test.tsx
+++ b/client/src/components/Planner/FileImportModal.test.tsx
@@ -2,6 +2,7 @@
 import { render, screen, fireEvent, waitFor } from '../../../tests/helpers/render';
 import { http, HttpResponse } from 'msw';
 import { server } from '../../../tests/helpers/msw/server';
+import { readMultipart } from '../../../tests/helpers/multipart';
 import { useTripStore } from '../../store/tripStore';
 import { resetAllStores, seedStore } from '../../../tests/helpers/store';
 import { buildTrip } from '../../../tests/helpers/factories';
@@ -127,11 +128,11 @@ describe('FileImportModal', () => {
     let flags: Record<string, string> = {};
     server.use(
       http.post('/api/trips/3/places/import/gpx', async ({ request }) => {
-        const fd = await request.formData();
+        const { fields } = await readMultipart(request);
         flags = {
-          waypoints: String(fd.get('importWaypoints')),
-          routes: String(fd.get('importRoutes')),
-          tracks: String(fd.get('importTracks')),
+          waypoints: fields.importWaypoints,
+          routes: fields.importRoutes,
+          tracks: fields.importTracks,
         };
         return HttpResponse.json({ count: 4, skipped: 0, places: [{ id: 11 }, { id: 12 }] });
       }),
diff --git a/client/tests/helpers/multipart.ts b/client/tests/helpers/multipart.ts
new file mode 100644
index 000000000..cb1169573
--- /dev/null
+++ b/client/tests/helpers/multipart.ts
@@ -0,0 +1,42 @@
+/**
+ * Reads the fields of a multipart request body without going through
+ * `Request.formData()`.
+ *
+ * Uploads in this app go out through axios' XHR adapter, and the body jsdom
+ * produces for that is one Node's multipart parser refuses on the CI runner
+ * (Node 24) while accepting it locally (Node 22) — the handler then throws
+ * before it ever sees a field. Reading the raw payload keeps the assertion on
+ * what was actually sent and takes the parser out of the picture.
+ *
+ * The body is a stream and can only be read once, so this returns everything in
+ * one pass. File parts are reported by filename rather than by content.
+ */
+export interface MultipartBody {
+  /** Plain text fields, by name. */
+  fields: Record<string, string>;
+  /** Names of the uploaded files, in the order they were appended. */
+  filenames: string[];
+}
+
+export async function readMultipart(request: Request): Promise<MultipartBody> {
+  const body = await request.text();
+  const boundary = request.headers.get('content-type')?.match(/boundary=(?:"([^"]+)"|([^;]+))/i);
+  const marker = boundary ? `--${(boundary[1] ?? boundary[2]).trim()}` : null;
+
+  const fields: Record<string, string> = {};
+  const filenames: string[] = [];
+
+  // Without a boundary there is nothing reliable to split on — hand back an
+  // empty result so the assertion fails on the value rather than on a throw.
+  if (!marker) return { fields, filenames };
+
+  for (const part of body.split(marker).slice(1)) {
+    const name = part.match(/name="([^"]*)"/)?.[1];
+    if (!name) continue;
+    const filename = part.match(/filename="([^"]*)"/)?.[1];
+    if (filename !== undefined) { filenames.push(filename); continue; }
+    // Headers, blank line, then the value up to the trailing CRLF.
+    fields[name] = part.match(/\r?\n\r?\n([\s\S]*?)\r?\n?$/)?.[1] ?? '';
+  }
+  return { fields, filenames };
+}