diff --git a/packages/nice-grpc-web/karma.conf.ts b/packages/nice-grpc-web/karma.conf.ts
index 60c12d22..5a351830 100644
--- a/packages/nice-grpc-web/karma.conf.ts
+++ b/packages/nice-grpc-web/karma.conf.ts
@@ -50,7 +50,7 @@ export default (config: Config & Record<string, unknown>) => {
     certPath = path.resolve(__dirname, './test-server/cert/tls.crt');
     keyPath = path.resolve(__dirname, './test-server/cert/tls.key');
   } else {
-    hostname = 'localhost';
+    hostname = '127.0.0.1';
     certPath = path.resolve(__dirname, './test-server/cert/self-signed.crt');
     keyPath = path.resolve(__dirname, './test-server/cert/self-signed.key');
 
diff --git a/packages/nice-grpc-web/run-specs-jasmine.ts b/packages/nice-grpc-web/run-specs-jasmine.ts
index 216d80bb..f229db9b 100644
--- a/packages/nice-grpc-web/run-specs-jasmine.ts
+++ b/packages/nice-grpc-web/run-specs-jasmine.ts
@@ -29,7 +29,7 @@ jasmine.addReporter(new SpecReporter());
 const certPath = path.resolve(__dirname, './test-server/cert/self-signed.crt');
 const keyPath = path.resolve(__dirname, './test-server/cert/self-signed.key');
 
-const hostname = 'localhost';
+const hostname = '127.0.0.1';
 const cert = selfsigned.generate([{name: 'commonName', value: hostname}], {
   keySize: 2048,
 });
diff --git a/packages/nice-grpc-web/test-server/client.ts b/packages/nice-grpc-web/test-server/client.ts
index 260eac21..8525b82b 100644
--- a/packages/nice-grpc-web/test-server/client.ts
+++ b/packages/nice-grpc-web/test-server/client.ts
@@ -26,7 +26,7 @@ export async function startRemoteTestServer(
   proxyType: 'grpcwebproxy' | 'envoy' | 'traefik' = 'grpcwebproxy',
   protocol: 'http' | 'https' = 'http',
 ): Promise<RemoteTestServer> {
-  const hostname = globalThis.location?.hostname ?? 'localhost';
+  const hostname = globalThis.location?.hostname ?? '127.0.0.1';
 
   const ws = new WebSocket(
     `ws://${hostname}:3000/mock-server?proxy=${proxyType}&protocol=${protocol}`,
diff --git a/packages/nice-grpc-web/test-server/grpcwebproxy.ts b/packages/nice-grpc-web/test-server/grpcwebproxy.ts
index a2ad10a8..80f4683c 100644
--- a/packages/nice-grpc-web/test-server/grpcwebproxy.ts
+++ b/packages/nice-grpc-web/test-server/grpcwebproxy.ts
@@ -30,7 +30,7 @@ export async function startGrpcWebProxy(
         : [`--server_http_debug_port=${listenPort}`, `--run_tls_server=false`]),
 
       `--server_bind_address=0.0.0.0`,
-      `--backend_addr=localhost:${backendPort}`,
+      `--backend_addr=127.0.0.1:${backendPort}`,
       `--use_websockets=true`,
       `--allow_all_origins=true`,
     ],