diff --git a/experimental/CHANGELOG.md b/experimental/CHANGELOG.md
index 32f6b55f929..e1627c9f914 100644
--- a/experimental/CHANGELOG.md
+++ b/experimental/CHANGELOG.md
@@ -11,6 +11,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 * feat(sdk-logs)!: add required `forceFlush()` to `LogRecordExporter` interface [#6356](https://github.com/open-telemetry/opentelemetry-js/pull/6356) @pichlermarc
   * (user-facing): `LogRecordExporter` interface now requires a `forceFlush()` method to be implemented. Custom exporters will need to implement this method to continue working with the Logs SDK.
 * feat(api-logs, sdk-logs)!: add Logger#enabled() [#6371](https://github.com/open-telemetry/opentelemetry-js/pull/6371) @david-luna
+* fix(opentelemetry-exporter-prometheus)!: default exporter host to localhost [#6599](https://github.com/open-telemetry/opentelemetry-js/pull/6599) @cjihrig
 
 ### :rocket: Features
 
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
index 1436b129524..e92f5a32f4c 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
@@ -19,7 +19,7 @@ import { URL } from 'url';
 
 export class PrometheusExporter extends MetricReader {
   static readonly DEFAULT_OPTIONS = {
-    host: undefined,
+    host: 'localhost',
     port: 9464,
     endpoint: '/metrics',
     prefix: '',
@@ -29,7 +29,7 @@ export class PrometheusExporter extends MetricReader {
     withoutTargetInfo: false,
   };
 
-  private readonly _host?: string;
+  private readonly _host: string;
   private readonly _port: number;
   private readonly _baseUrl: string;
   private readonly _endpoint: string;
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
index f413710505e..9c1fb98f093 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
@@ -44,6 +44,7 @@ describe('PrometheusExporter', () => {
   describe('constructor', () => {
     it('should construct an exporter', async () => {
       const exporter = new PrometheusExporter();
+      await exporter.startServer();
       assert.ok(typeof exporter.startServer === 'function');
       assert.ok(typeof exporter.shutdown === 'function');
       await exporter.shutdown();
@@ -95,6 +96,7 @@ describe('PrometheusExporter', () => {
       const port = PrometheusExporter.DEFAULT_OPTIONS.port;
       const endpoint = PrometheusExporter.DEFAULT_OPTIONS.endpoint;
       const exporter = new PrometheusExporter();
+      await exporter.startServer();
       const url = `http://localhost:${port}${endpoint}`;
       await request(url);
       await exporter.shutdown();
@@ -108,6 +110,7 @@ describe('PrometheusExporter', () => {
         port,
         endpoint,
       });
+      await exporter.startServer();
       const url = `http://localhost:${port}${endpoint}`;
       await request(url);
       await exporter.shutdown();
@@ -154,6 +157,7 @@ describe('PrometheusExporter', () => {
         port,
         endpoint,
       });
+      await exporter.startServer();
       const url = `http://localhost:${port}/invalid`;
 
       await assert.rejects(request(url), { statusCode: 404 });
@@ -194,6 +198,7 @@ describe('PrometheusExporter', () => {
 
     beforeEach(async () => {
       exporter = new PrometheusExporter();
+      await exporter.startServer();
       meterProvider = new MeterProvider({
         readers: [exporter],
       });
@@ -459,7 +464,8 @@ describe('PrometheusExporter', () => {
     let counter: Counter;
     let exporter: PrometheusExporter;
 
-    function setup(reader: PrometheusExporter) {
+    async function setup(reader: PrometheusExporter) {
+      await reader.startServer();
       meterProvider = new MeterProvider({
         readers: [exporter],
       });
@@ -477,7 +483,7 @@ describe('PrometheusExporter', () => {
       exporter = new PrometheusExporter({
         prefix: 'test_prefix',
       });
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:9464/metrics');
       const lines = body.split('\n');
 
@@ -495,7 +501,7 @@ describe('PrometheusExporter', () => {
         port: 8080,
       });
 
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:8080/metrics');
       const lines = body.split('\n');
 
@@ -513,7 +519,7 @@ describe('PrometheusExporter', () => {
         endpoint: '/test',
       });
 
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:9464/test');
       const lines = body.split('\n');
 
@@ -530,7 +536,7 @@ describe('PrometheusExporter', () => {
       exporter = new PrometheusExporter({
         appendTimestamp: true,
       });
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:9464/metrics');
       const lines = body.split('\n');
 
@@ -547,7 +553,7 @@ describe('PrometheusExporter', () => {
       exporter = new PrometheusExporter({
         withResourceConstantLabels: /.*/,
       });
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:9464/metrics');
       const lines = body.split('\n');
 
@@ -564,7 +570,7 @@ describe('PrometheusExporter', () => {
       exporter = new PrometheusExporter({
         withResourceConstantLabels: /telemetry.sdk.language|telemetry.sdk.name/,
       });
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:9464/metrics');
       const lines = body.split('\n');
 
@@ -579,7 +585,7 @@ describe('PrometheusExporter', () => {
 
     it('should omit target_info if withoutTargetInfo is true', async () => {
       exporter = new PrometheusExporter({ withoutTargetInfo: true });
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:9464/metrics');
 
       assert.deepStrictEqual(body.includes('target_info'), false);
@@ -587,7 +593,7 @@ describe('PrometheusExporter', () => {
 
     it('should omit scope labels if withoutScopeInfo is true', async () => {
       exporter = new PrometheusExporter({ withoutScopeInfo: true });
-      setup(exporter);
+      await setup(exporter);
       const body = await request('http://localhost:9464/metrics');
       const lines = body.split('\n');