diff --git a/.changeset/short-melons-tell.md b/.changeset/short-melons-tell.md
new file mode 100644
index 00000000000..158361683c7
--- /dev/null
+++ b/.changeset/short-melons-tell.md
@@ -0,0 +1,5 @@
+---
+'@graphql-tools/utils': patch
+---
+
+Fix build break in v8.13.0 in some ESM environments.
diff --git a/.eslintrc.cjs b/.eslintrc.cjs
index b58b87e0e73..9eeca768e43 100644
--- a/.eslintrc.cjs
+++ b/.eslintrc.cjs
@@ -4,8 +4,14 @@ module.exports = {
   parserOptions: {
     project: './tsconfig.json',
   },
-  extends: ['eslint:recommended', 'standard', 'prettier', 'plugin:@typescript-eslint/recommended'],
-  plugins: ['@typescript-eslint'],
+  extends: [
+    'eslint:recommended',
+    'standard',
+    'prettier',
+    'plugin:@typescript-eslint/recommended',
+    'plugin:import/typescript',
+  ],
+  plugins: ['@typescript-eslint', 'import'],
   rules: {
     'no-empty': 'off',
     'no-console': 'off',
@@ -94,6 +100,14 @@ module.exports = {
         'promise/param-names': 'off',
       },
     },
+    {
+      // Require extensions on all imports (other than package imports) outside
+      // of tests, as some ESM environments expect this when loading files.
+      // We don't check tests because they don't get compiled into the packages.
+      files: ['**/*.ts'],
+      excludedFiles: ['**/{test,tests,testing}/**/*.{ts,js}', '*.{spec,test}.{ts,js}'],
+      rules: { 'import/extensions': ['error', 'ignorePackages'] },
+    },
   ],
   ignorePatterns: [
     'dist',
diff --git a/packages/utils/src/Path.ts b/packages/utils/src/Path.ts
index 861975d7b01..5023238d26b 100644
--- a/packages/utils/src/Path.ts
+++ b/packages/utils/src/Path.ts
@@ -1,4 +1,4 @@
-import { Maybe } from './types';
+import { Maybe } from './types.js';
 
 export interface Path {
   readonly prev: Path | undefined;
diff --git a/packages/utils/src/jsutils.ts b/packages/utils/src/jsutils.ts
index 1d3e123b4c7..3006bfa0952 100644
--- a/packages/utils/src/jsutils.ts
+++ b/packages/utils/src/jsutils.ts
@@ -1,4 +1,4 @@
-import { MaybePromise } from './executor';
+import { MaybePromise } from './executor.js';
 
 export function isIterableObject(value: unknown): value is Iterable<unknown> {
   return value != null && typeof value === 'object' && Symbol.iterator in value;