diff --git a/.changeset/kind-lark-slim.md b/.changeset/kind-lark-slim.md
new file mode 100644
index 000000000000..fd5f29cad9fa
--- /dev/null
+++ b/.changeset/kind-lark-slim.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/node': patch
+---
+
+Fixes an infinite loop in `resolveClientDir()` when the server entry point is bundled with esbuild or similar tools. The function now throws a descriptive error instead of hanging indefinitely when the expected server directory segment is not found in the file path.
diff --git a/packages/integrations/node/src/shared.ts b/packages/integrations/node/src/shared.ts
index ddb59459ab05..d52c6879ced4 100644
--- a/packages/integrations/node/src/shared.ts
+++ b/packages/integrations/node/src/shared.ts
@@ -11,6 +11,10 @@ export const STATIC_HEADERS_FILE = '_headers.json';
  *
  * At build time, we know the relative path between server and client directories.
  * At runtime, we need to find the actual location based on where the server entry is running.
+ *
+ * ## Error
+ *
+ * It throws an error if it can't find the directory while walking the parent directories.
  */
 export function resolveClientDir(options: Options) {
 	// options.client and options.server are file:// URLs set at build time
@@ -26,7 +30,20 @@ export function resolveClientDir(options: Options) {
 	// We need to find the actual runtime location, not the build-time paths
 	const serverFolder = path.basename(options.server);
 	let serverEntryFolderURL = path.dirname(import.meta.url);
+	let previous = '';
 	while (!serverEntryFolderURL.endsWith(serverFolder)) {
+		// Guard against infinite loop
+		if (serverEntryFolderURL === previous) {
+			throw new Error(
+				`[@astrojs/node] Could not find the server directory "${serverFolder}" ` +
+					`by walking up from "${import.meta.url}". This can happen when the server ` +
+					`entry point is bundled into a single file (e.g. with esbuild) so that ` +
+					`import.meta.url no longer contains the original "${serverFolder}" path segment. ` +
+					`When bundling the server entry, make sure the output path contains a ` +
+					`"${serverFolder}" directory segment, or avoid bundling the server entry entirely.`,
+			);
+		}
+		previous = serverEntryFolderURL;
 		serverEntryFolderURL = path.dirname(serverEntryFolderURL);
 	}
 
diff --git a/packages/integrations/node/test/units/resolve-client-dir.test.js b/packages/integrations/node/test/units/resolve-client-dir.test.js
new file mode 100644
index 000000000000..fb2fd710d965
--- /dev/null
+++ b/packages/integrations/node/test/units/resolve-client-dir.test.js
@@ -0,0 +1,36 @@
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import { pathToFileURL } from 'node:url';
+import { resolveClientDir } from '../../dist/shared.js';
+
+describe('resolveClientDir', () => {
+	it('throws a descriptive error when the server folder is not found in the path', () => {
+		// Use pathToFileURL to build platform-valid file:// URLs. On Windows,
+		// file URLs require a drive letter (e.g. file:///C:/…); bare
+		// file:///project/… would cause fileURLToPath() to throw before the
+		// loop guard is reached.
+		const root = new URL('project/dist/', pathToFileURL('/'));
+		const client = new URL('client/', root).href;
+		const server = new URL('server/', root).href;
+
+		// When import.meta.url (of shared.js) does not contain a "server" segment,
+		// the while loop should terminate and throw instead of looping forever.
+		// This simulates what happens when the entry point is bundled with esbuild
+		// into a path that lacks the expected "server" directory segment.
+		assert.throws(
+			() =>
+				resolveClientDir({
+					client,
+					server,
+					mode: 'middleware',
+					host: false,
+					port: 4321,
+					staticHeaders: false,
+					bodySizeLimit: 0,
+				}),
+			{
+				message: /Could not find the server directory "server".*bundled into a single file/,
+			},
+		);
+	});
+});