diff --git a/packages/server/src/routes/api/files.ts b/packages/server/src/routes/api/files.ts
index ac3508d7c..f38165ca4 100644
--- a/packages/server/src/routes/api/files.ts
+++ b/packages/server/src/routes/api/files.ts
@@ -1,4 +1,4 @@
-import { ErrorNotFound, ErrorBadRequest } from '../../utils/errors';
+import { ErrorNotFound } from '../../utils/errors';
 import { File } from '../../db';
 import { bodyFields, formParse } from '../../utils/requestUtils';
 import { SubPath, respondWithFileContent } from '../../utils/routeUtils';
@@ -57,8 +57,12 @@ router.put('api/files/:id/content', async (path: SubPath, ctx: AppContext) => {
 	const fileModel = ctx.models.file({ userId: ctx.owner.id });
 	const fileId = path.id;
 	const result = await formParse(ctx.req);
-	if (!result?.files?.file) throw new ErrorBadRequest('File data is missing');
-	const buffer = await fs.readFile(result.files.file.path);
+
+	// When an app PUTs an empty file, `result.files` will be an emtpy object
+	// (could be the way Formidable parses the data?), but we still need to
+	// process the file so we set its content to an empty buffer.
+	// https://github.com/laurent22/joplin/issues/4402
+	const buffer = result?.files?.file ? await fs.readFile(result.files.file.path) : Buffer.alloc(0);
 
 	const file: File = await fileModel.entityFromItemId(fileId, { mustExist: false });
 	file.content = buffer;
diff --git a/packages/server/src/utils/requestUtils.ts b/packages/server/src/utils/requestUtils.ts
index 81a303838..093a14942 100644
--- a/packages/server/src/utils/requestUtils.ts
+++ b/packages/server/src/utils/requestUtils.ts
@@ -1,4 +1,4 @@
-import { ErrorBadRequest, ErrorForbidden } from './errors';
+import { ErrorForbidden } from './errors';
 import { AppContext } from './types';
 
 const formidable = require('formidable');
@@ -36,11 +36,17 @@ export async function formParse(req: any): Promise<FormParseResult> {
 }
 
 export async function bodyFields(req: any): Promise<BodyFields> {
+	// Formidable needs the content-type to be 'application/json' so on our side
+	// we explicitely set it to that. However save the previous value so that it
+	// can be restored.
+	let previousContentType = null;
 	if (req.headers['content-type'] !== 'application/json') {
-		throw new ErrorBadRequest(`Unsupported Content-Type: "${req.headers['content-type']}". Expected: "application/json"`);
+		previousContentType = req.headers['content-type'];
+		req.headers['content-type'] = 'application/json';
 	}
 
 	const form = await formParse(req);
+	if (previousContentType) req.headers['content-type'] = previousContentType;
 	return form.fields;
 }