diff --git a/packages/web/server/lib/notifications/routes.js b/packages/web/server/lib/notifications/routes.js
index d4c7b2c3..c4a2f5fa 100644
--- a/packages/web/server/lib/notifications/routes.js
+++ b/packages/web/server/lib/notifications/routes.js
@@ -172,6 +172,7 @@ export const registerNotificationRoutes = (app, dependencies) => {
     res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
     res.setHeader('Cache-Control', 'no-cache, no-transform');
     res.setHeader('Connection', 'keep-alive');
+    res.setHeader('X-Accel-Buffering', 'no');
     res.flushHeaders?.();
 
     const clients = getUiNotificationClients();
diff --git a/packages/web/server/lib/scheduled-tasks/routes.js b/packages/web/server/lib/scheduled-tasks/routes.js
index 590d65b3..98d7d36d 100644
--- a/packages/web/server/lib/scheduled-tasks/routes.js
+++ b/packages/web/server/lib/scheduled-tasks/routes.js
@@ -193,6 +193,7 @@ export const registerScheduledTaskRoutes = (app, dependencies) => {
     res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
     res.setHeader('Cache-Control', 'no-cache, no-transform');
     res.setHeader('Connection', 'keep-alive');
+    res.setHeader('X-Accel-Buffering', 'no');
     res.flushHeaders?.();
 
     const clients = getOpenChamberEventClients();
diff --git a/packages/web/server/sse-routes.test.js b/packages/web/server/sse-routes.test.js
new file mode 100644
index 00000000..a37f051b
--- /dev/null
+++ b/packages/web/server/sse-routes.test.js
@@ -0,0 +1,152 @@
+import { describe, expect, it } from 'bun:test';
+
+import { registerNotificationRoutes } from './lib/notifications/routes.js';
+import { registerScheduledTaskRoutes } from './lib/scheduled-tasks/routes.js';
+
+const createRouteRegistry = () => {
+  const routes = new Map();
+
+  return {
+    app: {
+      get(path, handler) {
+        routes.set(`GET ${path}`, handler);
+      },
+      post(path, handler) {
+        routes.set(`POST ${path}`, handler);
+      },
+      put(path, handler) {
+        routes.set(`PUT ${path}`, handler);
+      },
+      delete(path, handler) {
+        routes.set(`DELETE ${path}`, handler);
+      },
+    },
+    getRoute(method, path) {
+      return routes.get(`${method} ${path}`);
+    },
+  };
+};
+
+const createMockRequest = () => {
+  const listeners = new Map();
+
+  return {
+    headers: {},
+    on(event, handler) {
+      listeners.set(event, handler);
+      return this;
+    },
+    emit(event) {
+      const handler = listeners.get(event);
+      if (typeof handler === 'function') {
+        handler();
+      }
+    },
+  };
+};
+
+const createMockResponse = () => {
+  const headers = new Map();
+  let statusCode = 200;
+  let body = '';
+  let flushed = false;
+
+  return {
+    setHeader(name, value) {
+      headers.set(name.toLowerCase(), value);
+    },
+    getHeader(name) {
+      return headers.get(name.toLowerCase());
+    },
+    flushHeaders() {
+      flushed = true;
+    },
+    write(chunk) {
+      body += String(chunk);
+      return true;
+    },
+    status(code) {
+      statusCode = code;
+      return this;
+    },
+    json(payload) {
+      body += JSON.stringify(payload);
+      return this;
+    },
+    get statusCode() {
+      return statusCode;
+    },
+    get body() {
+      return body;
+    },
+    get flushed() {
+      return flushed;
+    },
+  };
+};
+
+describe('local SSE routes', () => {
+  it('serves notification SSE with nginx-safe headers', async () => {
+    const { app, getRoute } = createRouteRegistry();
+    const clients = new Set();
+
+    registerNotificationRoutes(app, {
+      uiAuthController: {
+        ensureSessionToken: async () => 'ui-token',
+      },
+      getUiSessionTokenFromRequest: () => 'ui-token',
+      getUiNotificationClients: () => clients,
+      writeSseEvent(res, payload) {
+        res.write(`data: ${JSON.stringify(payload)}\n\n`);
+      },
+    });
+
+    const handler = getRoute('GET', '/api/notifications/stream');
+    const req = createMockRequest();
+    const res = createMockResponse();
+
+    await handler(req, res);
+
+    expect(res.statusCode).toBe(200);
+    expect(res.getHeader('content-type')).toContain('text/event-stream');
+    expect(res.getHeader('cache-control')).toBe('no-cache, no-transform');
+    expect(res.getHeader('connection')).toBe('keep-alive');
+    expect(res.getHeader('x-accel-buffering')).toBe('no');
+    expect(res.flushed).toBe(true);
+    expect(res.body).toContain('openchamber:notification-stream-ready');
+    expect(clients.has(res)).toBe(true);
+
+    req.emit('close');
+    expect(clients.has(res)).toBe(false);
+  });
+
+  it('serves OpenChamber SSE with nginx-safe headers', () => {
+    const { app, getRoute } = createRouteRegistry();
+    const clients = new Set();
+
+    registerScheduledTaskRoutes(app, {
+      getOpenChamberEventClients: () => clients,
+      writeSseEvent(res, payload) {
+        res.write(`data: ${JSON.stringify(payload)}\n\n`);
+      },
+    });
+
+    const handler = getRoute('GET', '/api/openchamber/events');
+    const req = createMockRequest();
+    const res = createMockResponse();
+
+    handler(req, res);
+
+    expect(res.statusCode).toBe(200);
+    expect(res.getHeader('content-type')).toContain('text/event-stream');
+    expect(res.getHeader('cache-control')).toBe('no-cache, no-transform');
+    expect(res.getHeader('connection')).toBe('keep-alive');
+    expect(res.getHeader('x-accel-buffering')).toBe('no');
+    expect(res.flushed).toBe(true);
+    expect(res.body).toContain('openchamber:event-stream-ready');
+    expect(clients.has(res)).toBe(true);
+
+    req.emit('close');
+    expect(clients.has(res)).toBe(false);
+  });
+});