diff --git a/packages/ses/NEWS.md b/packages/ses/NEWS.md
index 75df0419a9..1716517358 100644
--- a/packages/ses/NEWS.md
+++ b/packages/ses/NEWS.md
@@ -13,6 +13,8 @@ User-visible changes in `ses`:
   - Node 18, Node 20, and all browsers have `structuredClone`
   - Node <= 16 have neither, but are also no longer supported by Endo.
 - Now exports separate layer for console shim: `ses/console-shim.js`.
+- Adds permits for `ModuleSource` if present, either the native implementation
+  or from `@endo/module-source/shim.js`.
 
 # v1.8.0 (2024-08-27)
 
diff --git a/packages/ses/src/get-anonymous-intrinsics.js b/packages/ses/src/get-anonymous-intrinsics.js
index f7fcd37118..1dc66f9825 100644
--- a/packages/ses/src/get-anonymous-intrinsics.js
+++ b/packages/ses/src/get-anonymous-intrinsics.js
@@ -161,5 +161,19 @@ export const getAnonymousIntrinsics = () => {
     );
   }
 
+  if (globalThis.ModuleSource) {
+    const AbstractModuleSourcePrototype = getPrototypeOf(
+      globalThis.ModuleSource.prototype,
+    );
+    intrinsics['%AbstractModuleSourcePrototype%'] =
+      AbstractModuleSourcePrototype;
+    intrinsics['%AbstractModuleSource%'] =
+      AbstractModuleSourcePrototype.constructor;
+  }
+
+  if (globalThis.ModuleSource) {
+    intrinsics['%ModuleSourcePrototype%'] = globalThis.ModuleSource.prototype;
+  }
+
   return intrinsics;
 };
diff --git a/packages/ses/src/permits.js b/packages/ses/src/permits.js
index 585d3c0c3f..9a06472cd1 100644
--- a/packages/ses/src/permits.js
+++ b/packages/ses/src/permits.js
@@ -101,8 +101,12 @@ export const universalPropertyNames = {
 
   // ESNext
 
+  // https://github.com/tc39/proposal-source-phase-imports?tab=readme-ov-file#js-module-source
+  ModuleSource: 'ModuleSource',
+
   lockdown: 'lockdown',
   harden: 'harden',
+
   HandledPromise: 'HandledPromise', // TODO: Until Promise.delegate (see below).
 };
 
@@ -1505,6 +1509,25 @@ export const permitted = {
     resolve: fn,
   },
 
+  // https://github.com/tc39/proposal-source-phase-imports?tab=readme-ov-file#js-module-source
+  '%AbstractModuleSourcePrototype%': {
+    constructor: '%AbstractModuleSource%',
+    '@@toStringTag': getter,
+  },
+  '%AbstractModuleSource%': {
+    '[[Proto]]': '%FunctionPrototype%',
+    prototype: '%AbstractModuleSourcePrototype%',
+  },
+  '%ModuleSourcePrototype%': {
+    '[[Proto]]': '%AbstractModuleSourcePrototype%',
+    constructor: 'ModuleSource',
+    '@@toStringTag': getter,
+  },
+  ModuleSource: {
+    '[[Proto]]': '%AbstractModuleSource%',
+    prototype: '%ModuleSourcePrototype%',
+  },
+
   Promise: {
     // Properties of the Promise Constructor
     '[[Proto]]': '%FunctionPrototype%',
diff --git a/packages/ses/test/module-source.test.js b/packages/ses/test/module-source.test.js
index dfdd0c2772..f2385ae9e6 100644
--- a/packages/ses/test/module-source.test.js
+++ b/packages/ses/test/module-source.test.js
@@ -6,6 +6,19 @@ import '@endo/module-source/shim.js';
 
 lockdown();
 
+test('module source property/prototype graph and hardening', t => {
+  const AbstractModuleSource = Object.getPrototypeOf(ModuleSource);
+  t.is(
+    Object.getPrototypeOf(ModuleSource.prototype),
+    AbstractModuleSource.prototype,
+  );
+
+  t.truthy(Object.isFrozen(ModuleSource));
+  t.truthy(Object.isFrozen(AbstractModuleSource));
+  t.truthy(Object.isFrozen(ModuleSource.prototype));
+  t.truthy(Object.isFrozen(AbstractModuleSource.prototype));
+});
+
 test('module source constructor', t => {
   const msr = new ModuleSource(`
     import foo from 'import-default-export-from-me.js';