diff --git a/packages/angular_devkit/build_angular/src/builders/dev-server/specs/works_spec.ts b/packages/angular_devkit/build_angular/src/builders/dev-server/specs/works_spec.ts
index 90ef75c2274b..edac384cca34 100644
--- a/packages/angular_devkit/build_angular/src/builders/dev-server/specs/works_spec.ts
+++ b/packages/angular_devkit/build_angular/src/builders/dev-server/specs/works_spec.ts
@@ -34,7 +34,7 @@ describe('Dev Server Builder', () => {
     expect(output.success).toBe(true);
 
     // When webpack-dev-server doesn't have `contentBase: false`, this will serve the repo README.
-    const response = await fetch('http://localhost:4200/README.md', {
+    const response = await fetch(`http://localhost:${output.port}/README.md`, {
       headers: {
         'Accept': 'text/html',
       },
diff --git a/tests/legacy-cli/e2e/utils/project.ts b/tests/legacy-cli/e2e/utils/project.ts
index 200f14dcfbce..8a06b02b0eae 100644
--- a/tests/legacy-cli/e2e/utils/project.ts
+++ b/tests/legacy-cli/e2e/utils/project.ts
@@ -165,9 +165,17 @@ export function useCIDefaults(projectName = 'test-project') {
     const appTargets = project.targets || project.architect;
     appTargets.build.options.progress = false;
     appTargets.test.options.progress = false;
-    // Disable auto-updating webdriver in e2e.
     if (appTargets.e2e) {
+      // Disable auto-updating webdriver in e2e.
       appTargets.e2e.options.webdriverUpdate = false;
+      // Use a random port in e2e.
+      appTargets.e2e.options.port = 0;
+    }
+
+    if (appTargets.serve) {
+      // Use a random port in serve.
+      appTargets.serve.options ??= {};
+      appTargets.serve.options.port = 0;
     }
   });
 }