diff --git a/packages/jest-transform/__tests__/__snapshots__/index.test.js.snap b/packages/jest-transform/__tests__/__snapshots__/index.test.mjs.snap
similarity index 100%
rename from packages/jest-transform/__tests__/__snapshots__/index.test.js.snap
rename to packages/jest-transform/__tests__/__snapshots__/index.test.mjs.snap
diff --git a/packages/jest-transform/__tests__/index.test.js b/packages/jest-transform/__tests__/index.test.mjs
similarity index 100%
rename from packages/jest-transform/__tests__/index.test.js
rename to packages/jest-transform/__tests__/index.test.mjs
diff --git a/packages/jest-transform/jest.config.mjs b/packages/jest-transform/jest.config.mjs
index 92696ee..47d90cc 100644
--- a/packages/jest-transform/jest.config.mjs
+++ b/packages/jest-transform/jest.config.mjs
@@ -157,10 +157,10 @@ const config = {
   // testLocationInResults: false,
 
   // The glob patterns Jest uses to detect test files
-  // testMatch: [
-  //   "**/__tests__/**/*.[jt]s?(x)",
-  //   "**/?(*.)+(spec|test).[tj]s?(x)",
-  // ],
+  testMatch: [
+    "**/__tests__/**/*.(m)[jt]s?(x)",
+    //   "**/?(*.)+(spec|test).[tj]s?(x)",
+  ],
 
   // An array of regexp pattern strings that are matched against all test paths, matched tests are skipped
   // testPathIgnorePatterns: [
diff --git a/packages/jest-transform/package.json b/packages/jest-transform/package.json
index 67481fd..8c252fb 100644
--- a/packages/jest-transform/package.json
+++ b/packages/jest-transform/package.json
@@ -7,7 +7,6 @@
     "url": "https://github.com/uhyo/nitrogql.git",
     "directory": "packages/jest-transform"
   },
-  "type": "module",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
   "exports": {
diff --git a/packages/jest-transform/src/index.ts b/packages/jest-transform/src/index.ts
index 896826d..3356763 100644
--- a/packages/jest-transform/src/index.ts
+++ b/packages/jest-transform/src/index.ts
@@ -1,11 +1,13 @@
 import { readFileSync } from "node:fs";
-import type { SyncTransformer, TransformedSource } from "@jest/transform";
-import { executeConfigFileSync } from "@nitrogql/core";
-import { init } from "@nitrogql/loader-core";
+import type {
+  SyncTransformer,
+  TransformedSource,
+  TransformerCreator,
+} from "@jest/transform";
 
-const { initiateTask, getLog } = await init();
-
-let lastLoadedConfigPath: string | undefined = undefined;
+// Note: this package uses CommonJS because jest-chain-transform does not support loading
+// ESM modules.
+// See: https://github.com/anc95/jest-chain-transform/issues/11
 
 export type TransformerConfig = {
   /**
@@ -14,43 +16,56 @@ export type TransformerConfig = {
   configFile?: string;
 };
 
-const transformer: SyncTransformer<TransformerConfig> = {
-  process(sourceText, sourcePath, options): TransformedSource {
-    const configFile = options.transformerConfig.configFile;
-    const task = initiateTask(sourcePath, sourceText);
-
-    if (lastLoadedConfigPath !== configFile && configFile) {
-      const configFileSource = configFileIsJS(configFile)
-        ? executeConfigFileSync(configFile)
-        : readFileSync(configFile, "utf-8");
-      task.loadConfig(configFileSource);
-    }
-    lastLoadedConfigPath = configFile;
-
-    while (true) {
-      const status = task.status();
-      switch (status.status) {
-        case "fileRequired": {
-          const requiredFiles = status.files;
-          for (const requiredFile of requiredFiles) {
-            const requiredFileSource = readFileSync(requiredFile, "utf-8");
-            task.supplyFile(requiredFile, requiredFileSource);
+const createTransformer: TransformerCreator<
+  SyncTransformer<TransformerConfig>,
+  TransformerConfig
+> = async () => {
+  const { init } = await import("@nitrogql/loader-core");
+  const { executeConfigFileSync } = await import("@nitrogql/core");
+  const { initiateTask, getLog } = await init();
+
+  let lastLoadedConfigPath: string | undefined = undefined;
+  const transformer: SyncTransformer<TransformerConfig> = {
+    process(sourceText, sourcePath, options): TransformedSource {
+      const configFile = options.transformerConfig.configFile;
+      const task = initiateTask(sourcePath, sourceText);
+
+      if (lastLoadedConfigPath !== configFile && configFile) {
+        const configFileSource = configFileIsJS(configFile)
+          ? executeConfigFileSync(configFile)
+          : readFileSync(configFile, "utf-8");
+        task.loadConfig(configFileSource);
+      }
+      lastLoadedConfigPath = configFile;
+
+      while (true) {
+        const status = task.status();
+        switch (status.status) {
+          case "fileRequired": {
+            const requiredFiles = status.files;
+            for (const requiredFile of requiredFiles) {
+              const requiredFileSource = readFileSync(requiredFile, "utf-8");
+              task.supplyFile(requiredFile, requiredFileSource);
+            }
+            break;
+          }
+          case "ready": {
+            const result = task.emit();
+            task.free();
+            return {
+              code: result,
+            };
           }
-          break;
-        }
-        case "ready": {
-          const result = task.emit();
-          task.free();
-          return {
-            code: result,
-          };
         }
       }
-    }
-  },
+    },
+  };
+  return transformer;
 };
 
-export default transformer;
+export default {
+  createTransformer,
+};
 
 function configFileIsJS(configFile: string) {
   return /\.[cm]?[jt]s$/.test(configFile);