diff --git a/packages/compartment-mapper/package.json b/packages/compartment-mapper/package.json
index 497dfbd8c8..667867aa93 100644
--- a/packages/compartment-mapper/package.json
+++ b/packages/compartment-mapper/package.json
@@ -58,6 +58,7 @@
     "@endo/cjs-module-analyzer": "^1.0.5",
     "@endo/module-source": "^0.0.0",
     "@endo/zip": "^1.0.5",
+    "@swc/wasm-typescript": "^1.7.2",
     "ses": "^1.5.0"
   },
   "devDependencies": {
diff --git a/packages/compartment-mapper/src/import-parsers.js b/packages/compartment-mapper/src/import-parsers.js
index 99c5f04cc5..2bf42a1773 100644
--- a/packages/compartment-mapper/src/import-parsers.js
+++ b/packages/compartment-mapper/src/import-parsers.js
@@ -11,11 +11,13 @@ import parserText from './parse-text.js';
 import parserBytes from './parse-bytes.js';
 import parserCjs from './parse-cjs.js';
 import parserMjs from './parse-mjs.js';
+import parserMts from './parse-mts.js';
 
 /** @satisfies {Readonly<ParserForLanguage>} */
 export const defaultParserForLanguage = Object.freeze(
   /** @type {const} */ ({
     mjs: parserMjs,
+    mts: parserMts,
     cjs: parserCjs,
     json: parserJson,
     text: parserText,
diff --git a/packages/compartment-mapper/src/node-modules.js b/packages/compartment-mapper/src/node-modules.js
index 786d93a06d..40764196d1 100644
--- a/packages/compartment-mapper/src/node-modules.js
+++ b/packages/compartment-mapper/src/node-modules.js
@@ -184,6 +184,7 @@ const findPackage = async (readDescriptor, canonical, directory, name) => {
 
 const defaultLanguages = /** @type {const} */ ([
   'mjs',
+  'mts',
   'cjs',
   'json',
   'text',
@@ -192,6 +193,7 @@ const defaultLanguages = /** @type {const} */ ([
 const defaultUncontroversialParsers = /** @type {const} */ ({
   cjs: 'cjs',
   mjs: 'mjs',
+  mts: 'mts',
   json: 'json',
   text: 'text',
   bytes: 'bytes',
diff --git a/packages/compartment-mapper/src/parse-mts.js b/packages/compartment-mapper/src/parse-mts.js
new file mode 100644
index 0000000000..760f8fdc43
--- /dev/null
+++ b/packages/compartment-mapper/src/parse-mts.js
@@ -0,0 +1,43 @@
+/* Provides language behavior (a parser) for importing ESM. */
+
+// @ts-check
+
+import { transform } from '@swc/wasm-typescript';
+import { ModuleSource } from '@endo/module-source';
+
+const textDecoder = new TextDecoder();
+
+/** @type {import('./types.js').ParseFn} */
+export const parseMts = async (
+  bytes,
+  _specifier,
+  sourceUrl,
+  _packageLocation,
+  options = {},
+) => {
+  const { sourceMap, sourceMapHook } = options;
+  const source = textDecoder.decode(bytes);
+  const transformed = await transform(source, {
+    filename: sourceUrl,
+    mode: 'strip-only',
+    module: true,
+  });
+  const record = new ModuleSource(transformed.code, {
+    sourceUrl,
+    // XXX use transformed source map?
+    sourceMap,
+    sourceMapUrl: sourceUrl,
+    sourceMapHook,
+  });
+  return {
+    parser: 'mts',
+    bytes,
+    record,
+  };
+};
+
+/** @type {import('./types.js').ParserImplementation} */
+export default {
+  parse: parseMts,
+  heuristicImports: false,
+};
diff --git a/packages/compartment-mapper/test/fixtures-esm-imports-cjs-define/0.mts b/packages/compartment-mapper/test/fixtures-esm-imports-cjs-define/0.mts
new file mode 100644
index 0000000000..682fc4bd44
--- /dev/null
+++ b/packages/compartment-mapper/test/fixtures-esm-imports-cjs-define/0.mts
@@ -0,0 +1,4 @@
+import { meaning } from './1.cjs';
+if (meaning !== 42) {
+  throw new Error('Fail');
+}
diff --git a/packages/compartment-mapper/test/mts-imports-cjs-define.test.js b/packages/compartment-mapper/test/mts-imports-cjs-define.test.js
new file mode 100644
index 0000000000..2817fb126c
--- /dev/null
+++ b/packages/compartment-mapper/test/mts-imports-cjs-define.test.js
@@ -0,0 +1,23 @@
+/* eslint-disable no-underscore-dangle */
+// import "./ses-lockdown.js";
+import 'ses';
+import test from 'ava';
+
+import { scaffold } from './scaffold.js';
+
+const fixture = new URL(
+  'fixtures-esm-imports-cjs-define/0.mts',
+  import.meta.url,
+).toString();
+
+const assertFixture = t => t.pass();
+
+const fixtureAssertionCount = 1;
+
+scaffold(
+  'fixtures-esm-imports-cjs-define',
+  test,
+  fixture,
+  assertFixture,
+  fixtureAssertionCount,
+);
diff --git a/yarn.lock b/yarn.lock
index 748bddba0d..17b8c43353 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -319,6 +319,7 @@ __metadata:
     "@endo/cjs-module-analyzer": "npm:^1.0.5"
     "@endo/module-source": "npm:^0.0.0"
     "@endo/zip": "npm:^1.0.5"
+    "@swc/wasm-typescript": "npm:^1.7.2"
     ava: "npm:^6.1.3"
     babel-eslint: "npm:^10.1.0"
     c8: "npm:^7.14.0"
@@ -2599,6 +2600,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@swc/wasm-typescript@npm:^1.7.2":
+  version: 1.7.2
+  resolution: "@swc/wasm-typescript@npm:1.7.2"
+  checksum: 10c0/fb84874ff21865b5b563564026cdec2de16c69c8f659b7070a4a4f15b70d2a53b1f8a8bfc40e00f90933e4c6fad537f3976209cc2fbc79be2558fd0a138785d5
+  languageName: node
+  linkType: hard
+
 "@tootallnate/once@npm:2":
   version: 2.0.0
   resolution: "@tootallnate/once@npm:2.0.0"