diff --git a/src/langbot/templates/embed/widget.js b/src/langbot/templates/embed/widget.js
index a62c54a4c..f026ea900 100644
--- a/src/langbot/templates/embed/widget.js
+++ b/src/langbot/templates/embed/widget.js
@@ -642,9 +642,10 @@
               .replace(/\s+/g, " ")
               .trim();
             if (
-              prevContent === content ||
-              prevContent.indexOf(content) >= 0 ||
-              content.indexOf(prevContent) >= 0
+              prevContent &&
+              (prevContent === content ||
+                prevContent.indexOf(content) >= 0 ||
+                content.indexOf(prevContent) >= 0)
             )
               return;
           }
diff --git a/web/tests/unit/embed-widget-assistant-dedupe.test.mjs b/web/tests/unit/embed-widget-assistant-dedupe.test.mjs
new file mode 100644
index 000000000..42f172d3d
--- /dev/null
+++ b/web/tests/unit/embed-widget-assistant-dedupe.test.mjs
@@ -0,0 +1,201 @@
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import path from 'node:path';
+import test from 'node:test';
+import vm from 'node:vm';
+import { fileURLToPath } from 'node:url';
+
+const testDirectory = path.dirname(fileURLToPath(import.meta.url));
+const widgetPath = path.resolve(
+  testDirectory,
+  '../../../src/langbot/templates/embed/widget.js',
+);
+const widgetSource = fs.readFileSync(widgetPath, 'utf8');
+
+class FakeElement {
+  constructor(tagName) {
+    this.tagName = tagName;
+    this.children = [];
+    this.className = '';
+    this.dataset = {};
+    this.style = {};
+    this.listeners = {};
+    this._innerHTML = '';
+  }
+
+  appendChild(child) {
+    this.children.push(child);
+    return child;
+  }
+
+  setAttribute(name, value) {
+    this[name] = String(value);
+  }
+
+  addEventListener(event, listener) {
+    this.listeners[event] = listener;
+  }
+
+  click() {
+    this.listeners.click?.({});
+  }
+
+  attachShadow() {
+    this.shadowRoot = new FakeElement('shadow-root');
+    return this.shadowRoot;
+  }
+
+  get classList() {
+    return {
+      add: (...names) => {
+        const classes = `${this.className} ${names.join(' ')}`
+          .trim()
+          .split(/\s+/);
+        this.className = [...new Set(classes)].join(' ');
+      },
+    };
+  }
+
+  set textContent(value) {
+    this._innerHTML = String(value ?? '');
+  }
+
+  set innerHTML(value) {
+    this._innerHTML = String(value ?? '');
+  }
+
+  get innerHTML() {
+    return this._innerHTML;
+  }
+
+  querySelectorAll(selector) {
+    const matches = [];
+    for (const child of this.children) {
+      if (
+        selector.startsWith('.') &&
+        child.className.split(/\s+/).includes(selector.slice(1))
+      ) {
+        matches.push(child);
+      }
+      matches.push(...child.querySelectorAll(selector));
+    }
+    return matches;
+  }
+
+  querySelector(selector) {
+    return this.querySelectorAll(selector)[0] ?? null;
+  }
+}
+
+class FakeDocument {
+  constructor() {
+    this.body = new FakeElement('body');
+    this.head = new FakeElement('head');
+    this.readyState = 'complete';
+    this.currentScript = { getAttribute: () => null };
+  }
+
+  createElement(tagName) {
+    return new FakeElement(tagName);
+  }
+
+  getElementById(id) {
+    const find = (element) => {
+      if (element.id === id) return element;
+      for (const child of element.children) {
+        const match = find(child);
+        if (match) return match;
+      }
+      return null;
+    };
+    return find(this.body) ?? find(this.head);
+  }
+}
+
+class FakeWebSocket {
+  static OPEN = 1;
+  static instances = [];
+
+  constructor(url) {
+    this.url = url;
+    this.readyState = FakeWebSocket.OPEN;
+    FakeWebSocket.instances.push(this);
+  }
+
+  send() {}
+}
+
+function launchWidget() {
+  FakeWebSocket.instances = [];
+  const document = new FakeDocument();
+  const window = {
+    crypto: { randomUUID: () => '00000000-0000-4000-8000-000000000000' },
+    sessionStorage: { getItem: () => null, setItem: () => {} },
+  };
+  const context = vm.createContext({
+    document,
+    window,
+    navigator: { clipboard: { writeText: () => Promise.resolve() } },
+    WebSocket: FakeWebSocket,
+    fetch: () => new Promise(() => {}),
+    requestAnimationFrame: () => 0,
+    setTimeout: () => 0,
+    clearTimeout: () => {},
+    setInterval: () => 0,
+    clearInterval: () => {},
+  });
+
+  vm.runInContext(widgetSource, context, { filename: widgetPath });
+  const root = document.getElementById('langbot-widget-root');
+  assert.ok(root, 'widget should initialize');
+  root.shadowRoot.querySelector('.lb-bubble').click();
+  const socket = FakeWebSocket.instances.at(-1);
+  assert.ok(socket, 'opening widget should connect its WebSocket');
+
+  return {
+    receive(message) {
+      socket.onmessage({
+        data: JSON.stringify({ type: 'response', data: message }),
+      });
+    },
+    assistantMessages() {
+      return root.shadowRoot.querySelectorAll('.lb-msg-assistant');
+    },
+  };
+}
+
+function assistant(id, content) {
+  return { id, role: 'assistant', content, is_final: true };
+}
+
+test('renders a non-empty reply after an empty assistant frame', () => {
+  const widget = launchWidget();
+
+  widget.receive(assistant('thought', ''));
+  widget.receive(assistant('answer', 'visible answer'));
+
+  const messages = widget.assistantMessages();
+  assert.equal(messages.length, 2);
+  assert.equal(
+    messages[1].querySelector('.lb-msg-bubble').innerHTML,
+    'visible answer',
+  );
+});
+
+test('still drops a duplicate non-empty assistant frame', () => {
+  const widget = launchWidget();
+
+  widget.receive(assistant('answer-1', 'same answer'));
+  widget.receive(assistant('answer-2', 'same answer'));
+
+  assert.equal(widget.assistantMessages().length, 1);
+});
+
+test('still keeps two distinct non-empty assistant frames', () => {
+  const widget = launchWidget();
+
+  widget.receive(assistant('answer-1', 'first answer'));
+  widget.receive(assistant('answer-2', 'second answer'));
+
+  assert.equal(widget.assistantMessages().length, 2);
+});