diff --git a/src/syntax.ts b/src/syntax.ts
index d823a01..05ecc17 100644
--- a/src/syntax.ts
+++ b/src/syntax.ts
@@ -4,7 +4,7 @@ import { readPackageJSON } from 'pkg-types'
 import { ResolveOptions, resolvePath } from './resolve'
 import { isNodeBuiltin, getProtocol } from './utils'
 
-const ESM_RE = /([\s;]|^)(import[\w,{}\s*]*from|import\s*['"*{]|export\b\s*(?:[*{]|default|type|function|const|var|let|async function)|import\.meta\b)/m
+const ESM_RE = /([\s;]|^)(import[\w,{}\s*]*from|import\s*['"*{]|export\b\s*(?:[*{]|default|class|type|function|const|var|let|async function)|import\.meta\b)/m
 
 const BUILTIN_EXTENSIONS = new Set(['.mjs', '.cjs', '.node', '.wasm'])
 
diff --git a/test/syntax.test.ts b/test/syntax.test.ts
index fd2f6a4..a7da182 100644
--- a/test/syntax.test.ts
+++ b/test/syntax.test.ts
@@ -20,6 +20,7 @@ const staticTests = {
   'export const a = 1': { hasESM: true, hasCJS: false, isMixed: false },
   'export function hi() {}': { hasESM: true, hasCJS: false, isMixed: false },
   'export async function foo() {}': { hasESM: true, hasCJS: false, isMixed: false },
+  'export class': { hasESM: true, hasCJS: false, isMixed: false },
   // CJS
   'exports.c={}': { hasESM: false, hasCJS: true, isMixed: false },
   'const b=true;module.exports={b};': { hasESM: false, hasCJS: true, isMixed: false },