diff --git a/kits/firestore-translate-text/CHANGELOG.md b/kits/firestore-translate-text/CHANGELOG.md
index bc1c5b451..293213e86 100644
--- a/kits/firestore-translate-text/CHANGELOG.md
+++ b/kits/firestore-translate-text/CHANGELOG.md
@@ -1,3 +1,4 @@
+- fix: a `null` input on update now fails the same way as the extension (a `TypeError` from `translateMultiple`, one error event, no write), instead of being routed to `translateSingle`.
 - fix: `onStart` and `onCompletion` are now published on every invocation, including a write event that arrives without change data; that path used to return before either event was recorded, so subscribers missed a lifecycle pair the extension always emitted.
 - Construct the translation client once per process instead of on every invocation, matching the legacy extension. This changes the exported `HandlerContext` type from `{ firestore, config, googleAiApiKey? }` to `{ config, service }`: `handleDocumentWrite` no longer builds the `TranslationService` itself and instead expects it on the context (build one with `createTranslationService`)
 - Initial release of kit, see README for differences between the legacy extension and this kit
diff --git a/kits/firestore-translate-text/src/translate/translateDocument.ts b/kits/firestore-translate-text/src/translate/translateDocument.ts
index 36e23bd50..78c5887e2 100644
--- a/kits/firestore-translate-text/src/translate/translateDocument.ts
+++ b/kits/firestore-translate-text/src/translate/translateDocument.ts
@@ -41,7 +41,7 @@ export const translateDocument = async (
     return;
   }
 
-  if (typeof input === "object" && input !== null) {
+  if (typeof input === "object") {
     return translateMultiple(
       input as Record<string, unknown>,
       languages,
diff --git a/kits/firestore-translate-text/tests/handlers.test.ts b/kits/firestore-translate-text/tests/handlers.test.ts
index 659e158f7..80d0c031c 100644
--- a/kits/firestore-translate-text/tests/handlers.test.ts
+++ b/kits/firestore-translate-text/tests/handlers.test.ts
@@ -342,6 +342,32 @@ describe("handleDocumentWrite", () => {
     expect(translateClassMethod).not.toHaveBeenCalled();
   });
 
+  test("fails without writing when an update sets the input to null", async () => {
+    const after = makeSnapshot({ input: null });
+
+    await expect(
+      handleDocumentWrite(
+        makeEvent(makeSnapshot({ input: "hello" }), after),
+        context()
+      )
+    ).resolves.toBeUndefined();
+
+    expect(logger.error).toHaveBeenCalledWith(
+      ...messages.error(expect.any(TypeError))
+    );
+    expect(logger.error).toHaveBeenCalledTimes(1);
+    expect(events.recordErrorEvent).toHaveBeenCalledWith(expect.any(TypeError));
+    expect(events.recordErrorEvent).toHaveBeenCalledTimes(1);
+    expect(logger.log).not.toHaveBeenCalledWith(
+      messages.translateInputStringToAllLanguages(
+        null as never,
+        defaultLanguages
+      )
+    );
+    expect(translateClassMethod).not.toHaveBeenCalled();
+    expect(firestore.update).not.toHaveBeenCalled();
+  });
+
   test("skips processing if there is no input on the before and after snapshots", async () => {
     const snapshot = makeSnapshot({ notTheInput: "hello" });
 
diff --git a/kits/firestore-translate-text/tests/translate-document.test.ts b/kits/firestore-translate-text/tests/translate-document.test.ts
index b668ef92b..f3b5bf052 100644
--- a/kits/firestore-translate-text/tests/translate-document.test.ts
+++ b/kits/firestore-translate-text/tests/translate-document.test.ts
@@ -18,11 +18,18 @@ import { beforeEach, describe, expect, test, vi } from "vitest";
 
 vi.mock("firebase-functions", () => import("./mocks/firebase-functions"));
 vi.mock("../src/events");
+vi.mock("../src/translate/translateMultiple", async (importOriginal) => {
+  const mod = await importOriginal<
+    typeof import("../src/translate/translateMultiple")
+  >();
+  return { ...mod, translateMultiple: vi.fn(mod.translateMultiple) };
+});
 
 import * as events from "../src/events";
 import { messages } from "../src/logs/messages";
 import type { TranslationService } from "../src/translate";
 import { translateDocument } from "../src/translate/translateDocument";
+import { translateMultiple } from "../src/translate/translateMultiple";
 import { translateSingle } from "../src/translate/translateSingle";
 import {
   defaultLanguages,
@@ -104,16 +111,22 @@ describe("translateDocument", () => {
     );
   });
 
-  test("treats a null input as a single translation, uncoerced", async () => {
+  test("routes a null input through translateMultiple, as the extension does", async () => {
     const snapshot = makeSnapshot({ input: null });
+    const service = makeService({ extractLanguages: vi.fn(() => ["en"]) });
 
-    await translateDocument(
+    await expect(
+      translateDocument(snapshot, service, makeConfig())
+    ).rejects.toThrow(TypeError);
+
+    expect(translateMultiple).toHaveBeenCalledWith(
+      null,
+      ["en"],
       snapshot,
-      makeService({ extractLanguages: vi.fn(() => ["en"]) }),
-      makeConfig()
+      service
     );
-
-    expect(translateString).toHaveBeenCalledWith(null, "en");
+    expect(translateString).not.toHaveBeenCalled();
+    expect(updateTranslations).not.toHaveBeenCalled();
   });
 
   test("exits early when the input field is a translation output path", async () => {