diff --git a/packages/astro/src/vite-plugin-config-alias/index.ts b/packages/astro/src/vite-plugin-config-alias/index.ts
index bd7a8e367102..f60da1e7ade0 100644
--- a/packages/astro/src/vite-plugin-config-alias/index.ts
+++ b/packages/astro/src/vite-plugin-config-alias/index.ts
@@ -142,6 +142,8 @@ export default function configAliasVitePlugin({
const replaceAliases = (match: string, importId: string) => {
if (!importId) return match;
+ // Skip data URIs — they are inline content, not file paths.
+ if (importId.startsWith('data:')) return match;
const resolved = resolveWithAlias(importId, configAlias);
if (resolved) {
diff --git a/packages/astro/test/alias-css-url-data-uri.test.ts b/packages/astro/test/alias-css-url-data-uri.test.ts
new file mode 100644
index 000000000000..4d2c07f78abb
--- /dev/null
+++ b/packages/astro/test/alias-css-url-data-uri.test.ts
@@ -0,0 +1,28 @@
+import assert from 'node:assert/strict';
+import { before, describe, it } from 'node:test';
+import * as cheerio from 'cheerio';
+import { type Fixture, loadFixture } from './test-utils.ts';
+
+// Regression test for https://github.com/withastro/astro/issues/17293
+// CSS url() with data URIs should not crash when tsconfig baseUrl is set.
+describe('CSS url() with data URIs and tsconfig baseUrl', () => {
+ let fixture: Fixture;
+
+ before(async () => {
+ fixture = await loadFixture({
+ root: './fixtures/alias-css-url-data-uri/',
+ });
+ await fixture.build();
+ });
+
+ it('preserves data URIs in url() without ENAMETOOLONG crash', async () => {
+ const html = await fixture.readFile('/index.html');
+ const $ = cheerio.load(html);
+
+ const styleTag = $('style').html() || '';
+ assert.ok(
+ styleTag.includes('data:image/svg+xml;base64,'),
+ 'CSS should preserve the data URI',
+ );
+ });
+});
diff --git a/packages/astro/test/fixtures/alias-css-url-data-uri/astro.config.mjs b/packages/astro/test/fixtures/alias-css-url-data-uri/astro.config.mjs
new file mode 100644
index 000000000000..d7ac4b718a29
--- /dev/null
+++ b/packages/astro/test/fixtures/alias-css-url-data-uri/astro.config.mjs
@@ -0,0 +1,2 @@
+import { defineConfig } from 'astro/config';
+export default defineConfig({});
diff --git a/packages/astro/test/fixtures/alias-css-url-data-uri/package.json b/packages/astro/test/fixtures/alias-css-url-data-uri/package.json
new file mode 100644
index 000000000000..d3325f2cb1be
--- /dev/null
+++ b/packages/astro/test/fixtures/alias-css-url-data-uri/package.json
@@ -0,0 +1,3 @@
+{
+ "name": "@test/alias-css-url-data-uri"
+}
diff --git a/packages/astro/test/fixtures/alias-css-url-data-uri/src/pages/index.astro b/packages/astro/test/fixtures/alias-css-url-data-uri/src/pages/index.astro
new file mode 100644
index 000000000000..101354a69734
--- /dev/null
+++ b/packages/astro/test/fixtures/alias-css-url-data-uri/src/pages/index.astro
@@ -0,0 +1,11 @@
+---
+
+---
+
+Hello
+
+
diff --git a/packages/astro/test/fixtures/alias-css-url-data-uri/tsconfig.json b/packages/astro/test/fixtures/alias-css-url-data-uri/tsconfig.json
new file mode 100644
index 000000000000..fb8ee3df7116
--- /dev/null
+++ b/packages/astro/test/fixtures/alias-css-url-data-uri/tsconfig.json
@@ -0,0 +1,5 @@
+{
+ "compilerOptions": {
+ "baseUrl": "."
+ }
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 866ff8491b60..bdd27e8ee8e7 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1917,6 +1917,8 @@ importers:
specifier: workspace:*
version: link:../../..
+ packages/astro/test/fixtures/alias-css-url-data-uri: {}
+
packages/astro/test/fixtures/alias-path-alias-style:
dependencies:
astro: