diff --git a/tsconfig.json b/tsconfig.json
index 217c19e1..a4756308 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -6,7 +6,7 @@
     // "incremental": true,                         /* Enable incremental compilation */
     "target": "ES6",                                /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
     "module": "es2015",                           /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
-    "lib": ["ES2015"],                                   /* Specify library files to be included in the compilation. */
+    "lib": ["es2015"],                                   /* Specify library files to be included in the compilation. */
     // "allowJs": true,                             /* Allow javascript files to be compiled. */
     // "checkJs": true,                             /* Report errors in .js files. */
     // "jsx": "preserve",                           /* Specify JSX code generation: 'preserve', 'react-native', 'react', 'react-jsx' or 'react-jsxdev'. */
@@ -68,5 +68,8 @@
     "skipLibCheck": true,                           /* Skip type checking of declaration files. */
     "forceConsistentCasingInFileNames": true        /* Disallow inconsistently-cased references to the same file. */
   },
-  "files": ["test/fetch/api.spec.ts"]
+  "files": [
+    "./index.d.ts",
+    "./test/fetch/api.spec.ts"
+  ]
 }