diff --git a/.agents/skills/verify-interface/features/README.md b/.agents/skills/verify-interface/features/README.md
index 20ba0ce..8856eb5 100644
--- a/.agents/skills/verify-interface/features/README.md
+++ b/.agents/skills/verify-interface/features/README.md
@@ -20,10 +20,6 @@ One file per feature. `covers:` lists every source file that computes something
 | [metadata](metadata.md) | A module author reads metadata and declares controllers. | effective-modes, declaration-errors, exports-runtime, consumer-compiles, derived-own-model, foreign-target-meta |
 | [smoke](smoke.md) | The fixed journey every verdict runs. | every-function, smoke-roundtrip |
 
-## Known issues, driven on purpose
-
-One journey fails on head and cites its issue: `issue-90-edit-index` ([#90](https://github.com/AntelopeJS/interface-data-api/issues/90)). A verdict that runs its feature is FAIL until the issue is fixed; the fix turns the journey green.
-
 ## Not driven
 
 Every documented behaviour of the README, `docs/` and the TSDoc has a journey above, or a row here with the reason.
diff --git a/.agents/skills/verify-interface/features/route-options.md b/.agents/skills/verify-interface/features/route-options.md
index 625f15a..1fb6a4c 100644
--- a/.agents/skills/verify-interface/features/route-options.md
+++ b/.agents/skills/verify-interface/features/route-options.md
@@ -38,7 +38,7 @@ A route is customized with `DefaultRoutes.WithOptions`; its options win over the
 
 - `option-overrides`: `maxPage` caps the `limit` of a query and is the page size without one, `noMandatory` as a route option lets a mandatory field be cleared while the plain route refuses it, any non-empty string (`"false"` included) turns the option on, `index` reads through a secondary index, `noPluck` still answers only readable fields, and a `pluckMode` no field declares answers `No fields found for pluckMode 'nothing'`.
 - `list-unknown`: a list route with `noPluck` answers 200 for a `pluckMode` no field declares, and a URL no route matches answers 404.
-- `issue-90-edit-index`: fails on purpose until [#90](https://github.com/AntelopeJS/interface-data-api/issues/90) is fixed: an `edit` with the `index` option updates the row the index found.
+- `issue-90-edit-index`: guards [#90](https://github.com/AntelopeJS/interface-data-api/issues/90): an `edit` with the `index` option updates the row the index found.
 - `no-mandatory-strings`: `noMandatory` skips the mandatory check for any non-empty string, `"false"` included, on `edit` and on `new`, and not for `""` or when absent.
 - `no-pluck-strings`: `noPluck` skips the pluck-mode check only when true.
 - `no-model-500`: a controller whose model reference holds no model answers 500.
diff --git a/.agents/skills/verify-interface/journeys-probe-1.ts b/.agents/skills/verify-interface/journeys-probe-1.ts
index c086916..a2786a2 100644
--- a/.agents/skills/verify-interface/journeys-probe-1.ts
+++ b/.agents/skills/verify-interface/journeys-probe-1.ts
@@ -128,7 +128,7 @@ export const readOverrides = shopJourney("a per-action read override hides or gr
   context.expect(row.folder, [equal("a write-only field is written on new", pick(row.rows[0] ?? null, "nickname"), "nn")]);
 });
 
-export const issue90 = shopJourney("fails on purpose until #90 is fixed: edit with the index option updates the row the index found", async (shop) => {
+export const issue90 = shopJourney("#90: edit with the index option updates the row the index found", async (shop) => {
   const { context } = shop;
   await seed(shop, PROBES);
   const edited = await shop.request("edit p1 by its tag", "PUT", "/probes/slugEdit?id=A", { body: '{"title":"New"}' });
diff --git a/docs/3.routes.md b/docs/3.routes.md
index 3709d91..b6bbf9c 100644
--- a/docs/3.routes.md
+++ b/docs/3.routes.md
@@ -263,10 +263,10 @@ The New route takes this option.
 
 The Edit route takes these options.
 
-| Option        | Type     | Description                                                                                                                          |
-| ------------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------ |
-| `index`       | `string` | Find the record and read the response through a secondary index. The update itself targets the record whose primary key equals `id`. |
-| `noMandatory` | `string` | Skip the mandatory field check                                                                                                       |
+| Option        | Type     | Description                                                                                                                |
+| ------------- | -------- | -------------------------------------------------------------------------------------------------------------------------- |
+| `index`       | `string` | Find the record through a secondary index instead of the primary key. The update and the response target the record found. |
+| `noMandatory` | `string` | Skip the mandatory field check                                                                                             |
 
 ## Amending the body of `new` and `edit`
 
diff --git a/src/index.ts b/src/index.ts
index 611d146..7bcbfcf 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -24,7 +24,7 @@ import {
 import type { WriteDocument } from "@antelopejs/interface-database/common";
 
 import { Parameters, Query, Validation } from "./components";
-import { isWriteDocument, isWriteValue } from "./internal/guards";
+import { isString, isWriteDocument, isWriteValue } from "./internal/guards";
 import { prototypeOf } from "./internal/prototypes";
 import { ReadProperties as readProperties } from "./internal/read-properties";
 import {
@@ -308,6 +308,8 @@ export namespace DefaultRoutes {
 
     const stored = await Query.Get(model.table, params.id, params.index);
     assert(stored, 404, "Not Found");
+    const { _id: primaryKey } = stored;
+    assert(isString(primaryKey), 500, "Stored row has no primary key");
 
     const dbData = await Query.WriteProperties(
       this,
@@ -319,11 +321,9 @@ export namespace DefaultRoutes {
     Validation.Lock(this, meta, dbData);
 
     triggerEvent(dbData, "update");
-    await model.table.get(params.id).update(writtenRow(dbData));
+    await model.table.get(primaryKey).update(writtenRow(dbData));
 
-    return readRow(this, meta, {
-      params: { id: params.id, index: params.index },
-    });
+    return readRow(this, meta, { params: { id: primaryKey } });
   }
 
   async function deleteRows(
diff --git a/src/tests/index/edit_index.test.ts b/src/tests/index/edit_index.test.ts
new file mode 100644
index 0000000..c314558
--- /dev/null
+++ b/src/tests/index/edit_index.test.ts
@@ -0,0 +1,97 @@
+import { expect } from "chai";
+import { Controller } from "@antelopejs/interface-api";
+import { Access, AccessMode, ModelReference } from "../../metadata";
+import {
+  DataController,
+  DefaultRoutes,
+  RegisterDataController,
+} from "../../index";
+import {
+  BasicDataModel,
+  Field,
+  Index,
+  Model,
+  RegisterSchema,
+  RegisterTable,
+  Table,
+} from "@antelopejs/interface-database-decorators";
+
+import { editRequest, getSchemaInstance } from "../utils";
+
+const TABLE = "edit-index-articles";
+const SCHEMA = "default";
+const LOCATION = "edit-index";
+
+@RegisterTable(TABLE, SCHEMA)
+class Article extends Table {
+  declare _id: string;
+
+  @Index()
+  @Field("string")
+  declare slug: string;
+
+  @Field("string")
+  declare title: string;
+}
+class ArticleModel extends BasicDataModel(Article, TABLE) {}
+
+@RegisterDataController()
+class _ArticleAPI extends DataController(
+  Article,
+  { edit: DefaultRoutes.WithOptions(DefaultRoutes.Edit, { index: "slug" }) },
+  Controller(`/${LOCATION}`),
+) {
+  @ModelReference()
+  @Model(ArticleModel)
+  declare model: ArticleModel;
+
+  @Access(AccessMode.ReadWrite)
+  declare slug: string;
+
+  @Access(AccessMode.ReadWrite)
+  declare title: string;
+}
+
+function articles() {
+  return getSchemaInstance(SCHEMA).table(TABLE);
+}
+
+describe("Edit with the index option", () => {
+  before(async () => {
+    await RegisterSchema(SCHEMA);
+    await articles().insert([
+      { _id: "a1", slug: "hello", title: "Old" },
+      { _id: "hello", slug: "decoy", title: "Decoy" },
+      { _id: "a2", slug: "rename-me", title: "Before" },
+    ]);
+  });
+
+  it("updates the row the index finds, not the row whose primary key is the id", async () => {
+    const response = await editRequest(
+      LOCATION,
+      { title: "New" },
+      { id: "hello" },
+    );
+    expect(response.status).to.equal(200);
+    expect(await response.json()).to.deep.include({ title: "New" });
+    expect(await articles().get("a1")).to.deep.include({ title: "New" });
+    expect(await articles().get("hello")).to.deep.include({ title: "Decoy" });
+  });
+
+  it("answers with the edited row when the edit changes the indexed field", async () => {
+    const response = await editRequest(
+      LOCATION,
+      { slug: "renamed", title: "After" },
+      { id: "rename-me" },
+    );
+    expect(response.status).to.equal(200);
+    expect(await response.json()).to.deep.include({
+      slug: "renamed",
+      title: "After",
+    });
+    expect(await articles().get("a2")).to.deep.include({
+      slug: "renamed",
+      title: "After",
+    });
+  });
+});