diff --git a/lib/commands/unipept/unipept_subcommand.ts b/lib/commands/unipept/unipept_subcommand.ts
index 09a62bde..56f9e1fc 100644
--- a/lib/commands/unipept/unipept_subcommand.ts
+++ b/lib/commands/unipept/unipept_subcommand.ts
@@ -20,6 +20,9 @@ export abstract class UnipeptSubcommand {
   selectedFields?: RegExp[];
   fasta: boolean;
 
+  // we must save this to be able to close it properly in tests
+  private streamInterface?: Interface;
+
   constructor(name: string) {
     this.name = name;
     const version = JSON.parse(readFileSync(new URL("../../../package.json", import.meta.url), "utf8")).version;
@@ -27,6 +30,7 @@ export abstract class UnipeptSubcommand {
     this.command = this.create(name);
     this.fasta = false;
   }
+
   abstract defaultBatchSize(): number;
 
   requiredFields(): string[] {
@@ -58,19 +62,17 @@ export abstract class UnipeptSubcommand {
       this.outputStream = createWriteStream(this.options.output);
     }
 
-    let slice = [];
-
-    for await (const input of this.getInputIterator(args, options.input)) {
-      slice.push(input);
-      if (slice.length >= this.batchSize) {
-        await this.processBatch(slice);
-        slice = [];
-      }
+    const iterator = this.getInputIterator(args, options.input);
+    const firstLine = (await iterator.next()).value;
+    if (firstLine.startsWith(">")) {
+      this.fasta = true;
+      await this.fastaInputProcessor(firstLine, iterator);
+    } else {
+      await this.normalInputProcessor(firstLine, iterator);
     }
-    await this.processBatch(slice);
   }
 
-  async processBatch(slice: string[]): Promise<void> {
+  async processBatch(slice: string[], fastaMapper?: { [key: string]: string }): Promise<void> {
     if (!this.formatter) throw new Error("Formatter not set");
 
     const r = await fetch(this.url as string, {
@@ -87,11 +89,44 @@ export abstract class UnipeptSubcommand {
       this.outputStream.write(this.formatter.header(result, this.fasta));
     }
 
-    this.outputStream.write(this.formatter.format(result, this.fasta, this.firstBatch));
+    this.outputStream.write(this.formatter.format(result, fastaMapper, this.firstBatch));
 
     if (this.firstBatch) this.firstBatch = false;
   }
 
+  async normalInputProcessor(firstLine: string, iterator: IterableIterator<string> | AsyncIterableIterator<string>) {
+    let slice = [firstLine];
+
+    for await (const line of iterator) {
+      slice.push(line);
+      if (slice.length >= this.batchSize) {
+        await this.processBatch(slice);
+        slice = [];
+      }
+    }
+    await this.processBatch(slice);
+  }
+
+  async fastaInputProcessor(firstLine: string, iterator: IterableIterator<string> | AsyncIterableIterator<string>) {
+    let currentFastaHeader = firstLine;
+    let slice = [];
+    let fastaMapper: { [key: string]: string } = {};
+    for await (const line of iterator) {
+      if (line.startsWith(">")) {
+        currentFastaHeader = line;
+      } else {
+        fastaMapper[line] = currentFastaHeader;
+        slice.push(line);
+        if (slice.length >= this.batchSize) {
+          await this.processBatch(slice, fastaMapper);
+          slice = [];
+          fastaMapper = {};
+        }
+      }
+    }
+    await this.processBatch(slice, fastaMapper);
+  }
+
   private constructRequestBody(slice: string[]): URLSearchParams {
     const names = this.getSelectedFields().length === 0 || this.getSelectedFields().some(regex => regex.toString().includes("name") || regex.toString().includes(".*$"));
     return new URLSearchParams({
@@ -128,13 +163,15 @@ export abstract class UnipeptSubcommand {
    * - if an input file is given, use the file
    * - otherwise, use standard input
    */
-  private getInputIterator(args: string[], input?: string): string[] | Interface {
+  private getInputIterator(args: string[], input?: string): IterableIterator<string> | AsyncIterableIterator<string> {
     if (args.length > 0) {
-      return args;
+      return args.values();
     } else if (input) {
-      return createInterface({ input: createReadStream(input) });
+      this.streamInterface = createInterface({ input: createReadStream(input) });
+      return this.streamInterface[Symbol.asyncIterator]();
     } else {
-      return createInterface({ input: process.stdin })
+      this.streamInterface = createInterface({ input: process.stdin });
+      return this.streamInterface[Symbol.asyncIterator]();
     }
   }
 
diff --git a/lib/formatters/formatter.ts b/lib/formatters/formatter.ts
index 1c8ecf02..d0ca6dca 100644
--- a/lib/formatters/formatter.ts
+++ b/lib/formatters/formatter.ts
@@ -4,15 +4,18 @@ export abstract class Formatter {
   abstract footer(): string;
   abstract convert(data: object[], first?: boolean): string;
 
-  format(data: object[], fastaMapper?: boolean, first?: boolean): string {
+  format(data: object[], fastaMapper?: { [key: string]: string }, first?: boolean): string {
     if (fastaMapper) {
-      data = this.integrateFastaHeaders(data, fastaMapper);
+      data = this.integrateFastaHeaders(data as { [key: string]: string }[], fastaMapper);
     }
     return this.convert(data, first);
   }
 
-  // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  integrateFastaHeaders(data: object[], fastaMapper: boolean): object[] {
+  integrateFastaHeaders(data: { [key: string]: string }[], fastaMapper: { [key: string]: string }): object[] {
+    const key = Object.keys(data[0])[0];
+    data.forEach((entry, i) => {
+      data[i] = Object.assign({ fasta_header: fastaMapper[entry[key]] }, entry);
+    });
     return data;
   }
 }
diff --git a/lib/formatters/to_xml.ts b/lib/formatters/to_xml.ts
index c40593b6..fb10ead4 100644
--- a/lib/formatters/to_xml.ts
+++ b/lib/formatters/to_xml.ts
@@ -250,6 +250,6 @@ function _isArray(array) {
   return array instanceof Array;
 }
 
-export function toXML(value: object, replacer?: function, space?: number | string): string {
-  return _toXML(value, replacer, space);
+export function toXML(value: object): string {
+  return _toXML(value);
 }
diff --git a/tests/commands/unipept/unipept_subcommand.test.ts b/tests/commands/unipept/unipept_subcommand.test.ts
index de816a36..1fde3605 100644
--- a/tests/commands/unipept/unipept_subcommand.test.ts
+++ b/tests/commands/unipept/unipept_subcommand.test.ts
@@ -1,4 +1,3 @@
-import { Interface } from 'readline';
 import { Pept2lca } from '../../../lib/commands/unipept/pept2lca';
 
 test('test command setup', () => {
@@ -28,19 +27,18 @@ test('test correct inputIterator', async () => {
   const command = new Pept2lca();
 
   // should be stdin
-  let input = command["getInputIterator"]([]) as Interface;
-  expect(input).toBeInstanceOf(Interface);
-  input.close();
+  let input = command["getInputIterator"]([]) as AsyncIterableIterator<string>;
+  expect(typeof input[Symbol.asyncIterator]).toBe("function");
+  command['streamInterface']?.close();
 
   // should be a (non-existant) file and error
-  input = command["getInputIterator"]([], "filename") as Interface;
-  input.on("error", (e) => {
-    expect(e.toString()).toMatch(/no such file/);
-  });
+  input = command["getInputIterator"]([], "filename") as AsyncIterableIterator<string>;
+  expect(typeof input[Symbol.asyncIterator]).toBe("function");
+  await expect(async () => { await input.next() }).rejects.toThrow(/no such file/);
 
   // should be array
-  const inputArray = command["getInputIterator"](["A", "B"]);
-  expect(inputArray).toBeInstanceOf(Array);
+  const inputArray = command["getInputIterator"](["A", "B"]) as IterableIterator<string>;
+  expect(typeof inputArray[Symbol.iterator]).toBe("function");
 });
 
 test('test selected fields parsing', () => {
diff --git a/tests/formatters/csv_formatter.test.ts b/tests/formatters/csv_formatter.test.ts
index 2b9a3b85..2ea80c37 100644
--- a/tests/formatters/csv_formatter.test.ts
+++ b/tests/formatters/csv_formatter.test.ts
@@ -23,8 +23,8 @@ test('test convert', () => {
 });
 
 test('test format with fasta', () => {
-  //const fasta = [['>test', '5']];
-  //const object = [TestObject.testObject(), TestObject.testObject()];
-  //const csv = [`>test,${TestObject.asCsv()}`, TestObject.asCsv(), ""].join("\n");
-  //expect(formatter.format(object, fasta, false)).toBe(csv);
+  const fasta = { 5: ">test" };
+  const object = [TestObject.testObject(), TestObject.testObject()];
+  const csv = [`>test,${TestObject.asCsv()}`, `>test,${TestObject.asCsv()}`, ""].join("\n");
+  expect(formatter.format(object, fasta, false)).toBe(csv);
 });
diff --git a/tests/formatters/formatter.test.ts b/tests/formatters/formatter.test.ts
new file mode 100644
index 00000000..c041f31b
--- /dev/null
+++ b/tests/formatters/formatter.test.ts
@@ -0,0 +1,12 @@
+import { FormatterFactory } from "../../lib/formatters/formatter_factory";
+import { TestObject } from "./test_object";
+
+test('test integrate fasta headers', async () => {
+  const formatter = FormatterFactory.getFormatter("csv");
+  const fasta = { 5: ">test" };
+  const object = [TestObject.testObject(), TestObject.testObject()];
+  const integrated = [Object.assign({ fasta_header: ">test" }, TestObject.testObject()), Object.assign({ fasta_header: ">test" }, TestObject.testObject())];
+  // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+  // @ts-ignore
+  expect(formatter.integrateFastaHeaders(object, fasta)).toEqual(integrated);
+});
diff --git a/tests/formatters/json_formatter.test.ts b/tests/formatters/json_formatter.test.ts
index c4e80648..42e14293 100644
--- a/tests/formatters/json_formatter.test.ts
+++ b/tests/formatters/json_formatter.test.ts
@@ -21,8 +21,8 @@ test('test convert', () => {
 });
 
 test('test format with fasta', () => {
-  //const fasta = [['>test', '5']];
-  //const object = [TestObject.testObject()];
-  //const json = '{"fasta_header":">test","integer":5,"string":"string","list":["a",2,false]}';
-  //expect(formatter.format(object, fasta, true)).toBe(json);
+  const fasta = { 5: ">test" };
+  const object = [TestObject.testObject()];
+  const json = '{"fasta_header":">test","integer":5,"string":"string","list":["a",2,false]}';
+  expect(formatter.format(object, fasta, true)).toBe(json);
 });
diff --git a/tests/formatters/xml_formatter.test.ts b/tests/formatters/xml_formatter.test.ts
index c327d034..6994861b 100644
--- a/tests/formatters/xml_formatter.test.ts
+++ b/tests/formatters/xml_formatter.test.ts
@@ -21,8 +21,8 @@ test('test convert', () => {
 });
 
 test('test format with fasta', () => {
-  //const fasta = [['>test', '5']];
-  //const object = [TestObject.testObject()];
-  //const json = '{"fasta_header":">test","integer":5,"string":"string","list":["a",2,false]}';
-  //expect(formatter.format(object, fasta, true)).toBe(json);
+  const fasta = { 5: ">test" };
+  const object = [TestObject.testObject()];
+  const xml = `<result><fasta_header>&gt;test</fasta_header>${TestObject.asXml()}</result>`;
+  expect(formatter.format(object, fasta, true)).toBe(xml);
 });