diff --git a/README.md b/README.md
index 92abc78..0a3be05 100644
--- a/README.md
+++ b/README.md
@@ -190,15 +190,15 @@ assertion syntax.
 
 The default configuration will recognize any file as a test file that...
 
-- has a `.test.*js*` extension (i.e. `.test.cjs`, `.test.js`, `.test.mjs`, or
-  `.test.ts`).
-- is not located in `node_modules`.
+- has `.test.` just before its file name extension (i.e. `example.test.js`).
+- is not located in the `node_modules` or `lib` directories.
 
 The sample code packages tests next to the source code they exercise. If you
 prefer to segregate your tests into a directory outside [`src`](./src/) (e.g.
 `test`), that will work as well.
 
-Either way, all test files will be excluded from the build.
+Either way, all test files meeting the above conditions will be excluded from
+the build.
 
 To enable `mocha`-specific linting in your test files, add the following
 directive at the top of every test file:
diff --git a/build.config.js b/build.config.js
new file mode 100644
index 0000000..a15acdf
--- /dev/null
+++ b/build.config.js
@@ -0,0 +1,6 @@
+const config = require('./babel.config');
+
+module.exports = (api) => ({
+  ...config(api),
+  ignore: [/\.test\.\w+$/],
+});
diff --git a/package.json b/package.json
index 904807b..2221828 100644
--- a/package.json
+++ b/package.json
@@ -60,7 +60,7 @@
     "require": [
       "@babel/register"
     ],
-    "spec": "**/*.test.*js*"
+    "spec": "**/*.test.!(*.*)"
   },
   "release-it": {
     "github": {
@@ -71,7 +71,7 @@
     }
   },
   "scripts": {
-    "build": "rimraf ./lib && babel src -d lib --ignore **/*.test.cjs,**/*.test.js,**/*.test.mjs,**/*.test.ts",
+    "build": "rimraf ./lib && babel src -d lib --config-file ./build.config.js",
     "release": "dotenv -c -- release-it",
     "test": "mocha"
   }