diff --git a/packages/angular/build/src/builders/unit-test/options.ts b/packages/angular/build/src/builders/unit-test/options.ts
index 3b003e9c3620..ac3d1b4e9652 100644
--- a/packages/angular/build/src/builders/unit-test/options.ts
+++ b/packages/angular/build/src/builders/unit-test/options.ts
@@ -127,7 +127,11 @@ export async function normalizeOptions(
     dumpVirtualFiles: options.dumpVirtualFiles,
     listTests: options.listTests,
     runnerConfig:
-      typeof runnerConfig === 'string' ? path.resolve(workspaceRoot, runnerConfig) : runnerConfig,
+      typeof runnerConfig === 'string'
+        ? runnerConfig.length === 0
+          ? true
+          : path.resolve(workspaceRoot, runnerConfig)
+        : runnerConfig,
   };
 }
 
diff --git a/packages/angular/build/src/builders/unit-test/schema.json b/packages/angular/build/src/builders/unit-test/schema.json
index ed766c1774a2..3b92d31a4cde 100644
--- a/packages/angular/build/src/builders/unit-test/schema.json
+++ b/packages/angular/build/src/builders/unit-test/schema.json
@@ -20,7 +20,7 @@
       "enum": ["karma", "vitest"]
     },
     "runnerConfig": {
-      "type": ["boolean", "string"],
+      "type": ["string", "boolean"],
       "description": "Specifies the configuration file for the selected test runner. If a string is provided, it will be used as the path to the configuration file. If `true`, the builder will search for a default configuration file (e.g., `vitest.config.ts` or `karma.conf.js`). If `false`, no external configuration file will be used.\\nFor Vitest, this enables advanced options and the use of custom plugins. Please note that while the file is loaded, the Angular team does not provide direct support for its specific contents or any third-party plugins used within it.",
       "default": false
     },
diff --git a/tests/legacy-cli/e2e/tests/vitest/runner-config-path.ts b/tests/legacy-cli/e2e/tests/vitest/runner-config-path.ts
new file mode 100644
index 000000000000..456469b2d6a4
--- /dev/null
+++ b/tests/legacy-cli/e2e/tests/vitest/runner-config-path.ts
@@ -0,0 +1,33 @@
+import assert from 'node:assert/strict';
+import path from 'node:path';
+import { writeMultipleFiles } from '../../utils/fs';
+import { ng } from '../../utils/process';
+import { applyVitestBuilder } from '../../utils/vitest';
+
+export default async function (): Promise<void> {
+  await applyVitestBuilder();
+
+  // Create a custom Vitest configuration file.
+  const customConfigPath = 'vitest.custom.mjs';
+  await writeMultipleFiles({
+    [customConfigPath]: `
+      import { defineConfig } from 'vitest/config';
+      export default defineConfig({
+        test: {
+          // A unique option to confirm this file is being used.
+          passWithNoTests: true,
+        },
+      });
+    `,
+  });
+
+  const absoluteConfigPath = path.resolve(customConfigPath);
+  const { stdout } = await ng('test', `--runner-config=${absoluteConfigPath}`);
+
+  // Assert that the CLI logs the use of the specified configuration file.
+  assert.match(
+    stdout,
+    /vitest\.custom\.mjs/,
+    'Expected a message confirming the use of the custom config file.',
+  );
+}