diff --git a/.changeset/bumpy-cats-sneeze.md b/.changeset/bumpy-cats-sneeze.md
new file mode 100644
index 000000000000..0aa6b4d30d2c
--- /dev/null
+++ b/.changeset/bumpy-cats-sneeze.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue where requests with query parameters to the `base` path would return a 404 if trailingSlash was not `'ignore'` in development
diff --git a/packages/astro/src/vite-plugin-astro-server/base.ts b/packages/astro/src/vite-plugin-astro-server/base.ts
index 11d9c66078af..23e04690fc2b 100644
--- a/packages/astro/src/vite-plugin-astro-server/base.ts
+++ b/packages/astro/src/vite-plugin-astro-server/base.ts
@@ -13,8 +13,10 @@ export function baseMiddleware(
 	logger: Logger,
 ): vite.Connect.NextHandleFunction {
 	const { config } = settings;
-	const site = config.site ? new URL(config.base, config.site) : undefined;
-	const devRootURL = new URL(config.base, 'http://localhost');
+	// The base may be an empty string by now, causing the URL creation to fail. We provide a default instead
+	const base = config.base || '/';
+	const site = config.site ? new URL(base, config.site) : undefined;
+	const devRootURL = new URL(base, 'http://localhost');
 	const devRoot = site ? site.pathname : devRootURL.pathname;
 	const devRootReplacement = devRoot.endsWith('/') ? '/' : '';
 
diff --git a/packages/astro/src/vite-plugin-astro-server/request.ts b/packages/astro/src/vite-plugin-astro-server/request.ts
index 4b6c683d11c7..c859e3d4c5fe 100644
--- a/packages/astro/src/vite-plugin-astro-server/request.ts
+++ b/packages/astro/src/vite-plugin-astro-server/request.ts
@@ -47,6 +47,12 @@ export async function handleRequest({
 		}
 	}
 
+	// Normalize root path to empty string when trailingSlash is 'never' and there's a non-root base
+	// This ensures consistent route matching for the index route (e.g., /base?query -> '')
+	if (config.trailingSlash === 'never' && pathname === '/' && config.base !== '/') {
+		pathname = '';
+	}
+
 	// Add config.base back to url before passing it to SSR
 	url.pathname = removeTrailingForwardSlash(config.base) + pathname;
 
diff --git a/packages/astro/test/units/routing/trailing-slash.test.js b/packages/astro/test/units/routing/trailing-slash.test.js
index 3a1c99df0ec7..ebb39d0a080b 100644
--- a/packages/astro/test/units/routing/trailing-slash.test.js
+++ b/packages/astro/test/units/routing/trailing-slash.test.js
@@ -213,6 +213,29 @@ describe('trailingSlash', () => {
 		assert.equal(res.statusCode, 404);
 	});
 
+	// Test for issue #15095: Query params should not cause 404 when base is set and trailingSlash is never
+	it('should match root path with query params when base is set and trailingSlash is never', async () => {
+		const { req, res, text } = createRequestAndResponse({
+			method: 'GET',
+			url: '/base?foo=bar',
+		});
+		baseContainer.handle(req, res);
+		const json = await text();
+		assert.equal(json, '{"success":true}');
+		assert.equal(res.statusCode, 200);
+	});
+
+	it('should match sub path with query params when base is set and trailingSlash is never', async () => {
+		const { req, res, text } = createRequestAndResponse({
+			method: 'GET',
+			url: '/base/injected?foo=bar',
+		});
+		baseContainer.handle(req, res);
+		const json = await text();
+		assert.equal(json, '{"success":true}');
+		assert.equal(res.statusCode, 200);
+	});
+
 	// Test for issue #13736: Astro.url.pathname should respect trailingSlash config with base
 	it('Astro.url.pathname should not have trailing slash on root path when base is set and trailingSlash is never', async () => {
 		const { req, res, text } = createRequestAndResponse({