diff --git a/packages/pg-esm-test/pg-protocol.test.js b/packages/pg-esm-test/pg-protocol.test.js
index 43df99de2..e06ca4beb 100644
--- a/packages/pg-esm-test/pg-protocol.test.js
+++ b/packages/pg-esm-test/pg-protocol.test.js
@@ -1,6 +1,7 @@
 import protocol, { NoticeMessage, DatabaseError } from 'pg-protocol/dist/messages.js'
 import { describe, it } from 'node:test'
 import { strict as assert } from 'assert'
+import { execFileSync } from 'node:child_process'
 
 describe('pg-protocol', () => {
   it('should export database error', () => {
@@ -15,4 +16,15 @@ describe('pg-protocol', () => {
   it('should export NoticeMessage from file in dist folder', () => {
     assert.ok(NoticeMessage)
   })
+  it('should load the ESM entry without module syntax detection', () => {
+    const flags = process.allowedNodeEnvironmentFlags.has('--experimental-detect-module')
+      ? ['--no-experimental-detect-module']
+      : []
+    const script =
+      "import { parse, serialize, DatabaseError } from 'pg-protocol'; if (!parse || !serialize || !DatabaseError) process.exit(1)"
+    execFileSync(process.execPath, [...flags, '--input-type=module', '-e', script], {
+      cwd: new URL('.', import.meta.url),
+      stdio: 'pipe',
+    })
+  })
 })
diff --git a/packages/pg-protocol/esm/index.js b/packages/pg-protocol/esm/index.mjs
similarity index 100%
rename from packages/pg-protocol/esm/index.js
rename to packages/pg-protocol/esm/index.mjs
diff --git a/packages/pg-protocol/package.json b/packages/pg-protocol/package.json
index 5caf29557..4ddbab7c4 100644
--- a/packages/pg-protocol/package.json
+++ b/packages/pg-protocol/package.json
@@ -6,7 +6,7 @@
   "types": "dist/index.d.ts",
   "exports": {
     ".": {
-      "import": "./esm/index.js",
+      "import": "./esm/index.mjs",
       "require": "./dist/index.js",
       "default": "./dist/index.js"
     },