diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 02bd155..dd3d940 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -34,7 +34,7 @@ The app runs at [http://localhost:3000](http://localhost:3000). There is no back
 | `pnpm dev`           | Start the dev server with hot reload                                                |
 | `pnpm build`         | Production build (must pass before merging)                                         |
 | `pnpm start`         | Serve the production build locally                                                  |
-| `pnpm lint`          | ESLint (Next.js + TypeScript rules)                                                 |
+| `pnpm lint`          | ESLint (Next.js + TypeScript rules); any warning fails it, like an error            |
 | `pnpm typecheck`     | `tsc --noEmit` in strict mode                                                       |
 | `pnpm test`          | Unit tests with Vitest (`lib/**` and `packages/*/src/**`)                           |
 | `pnpm test:e2e`      | Playwright tests against the production build: routes, flows, axe (see below)       |
diff --git a/lib/color/matrix.test.ts b/lib/color/matrix.test.ts
index 325048e..68c496b 100644
--- a/lib/color/matrix.test.ts
+++ b/lib/color/matrix.test.ts
@@ -1,11 +1,12 @@
 import { describe, expect, test, vi } from "vitest";
 
+import type * as ColorModule from "@/lib/color/color";
 import { apcaContrast, fromHex } from "@/lib/color/color";
 import { apcaLevel, matrixCell } from "@/lib/color/matrix";
 
 // Pass through to the real implementation, but let a test pin an exact Lc for one call.
 vi.mock("@/lib/color/color", async (importOriginal) => {
-  const actual = await importOriginal<typeof import("@/lib/color/color")>();
+  const actual = await importOriginal<typeof ColorModule>();
   return { ...actual, apcaContrast: vi.fn(actual.apcaContrast) };
 });
 
diff --git a/package.json b/package.json
index 20fe1a3..ea96ce0 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
     "build": "next build",
     "postbuild": "node scripts/generate-service-worker.mjs",
     "start": "next start",
-    "lint": "eslint .",
+    "lint": "eslint . --max-warnings 0",
     "typecheck": "tsc --noEmit",
     "test": "vitest run",
     "test:e2e": "playwright test",