diff --git a/packages/compartment-mapper/src/node-modules.js b/packages/compartment-mapper/src/node-modules.js
index ef1f183d00..7a9f7c27c1 100644
--- a/packages/compartment-mapper/src/node-modules.js
+++ b/packages/compartment-mapper/src/node-modules.js
@@ -547,6 +547,11 @@ const gatherDependency = async (
   );
 };
 
+/**
+ * The name used by a root entry compartment that has no `name` in its package descriptor.
+ */
+export const ANONYMOUS_COMPARTMENT = '<ANONYMOUS>';
+
 /**
  * graphPackages returns a graph whose keys are nominally URLs, one per
  * package, with values that are label: (an informative Compartment name, built
@@ -621,6 +626,15 @@ const graphPackages = async (
     };
   }
 
+  /**
+   * If the entry package descriptor has no `name`, we need to put _something_
+   * in there to pass compartment map validation (go find
+   * `assertCompartmentMap()`).
+   */
+  if (!packageDescriptor.name) {
+    packageDescriptor.name = ANONYMOUS_COMPARTMENT;
+  }
+
   const graph = create(null);
   await graphPackage(
     packageDescriptor.name,
diff --git a/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/incognito/index.js b/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/incognito/index.js
new file mode 100644
index 0000000000..32802f71ae
--- /dev/null
+++ b/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/incognito/index.js
@@ -0,0 +1 @@
+export default 'doctor emilio lizardo';
diff --git a/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/incognito/package.json b/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/incognito/package.json
new file mode 100644
index 0000000000..aead43de36
--- /dev/null
+++ b/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/incognito/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
\ No newline at end of file
diff --git a/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/package.json b/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/package.json
new file mode 100644
index 0000000000..7d092e9795
--- /dev/null
+++ b/packages/compartment-mapper/test/fixtures-anonymous/node_modules/unnamed/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "unnamed",
+  "version": "1.0.0",
+  "exports": {
+    "./incognito": "./incognito/index.js"
+  },
+  "type": "commonjs",
+  "scripts": {
+    "preinstall": "echo DO NOT INSTALL TEST FIXTURES; exit -1"
+  }
+}
diff --git a/packages/compartment-mapper/test/node-modules.test.js b/packages/compartment-mapper/test/node-modules.test.js
new file mode 100644
index 0000000000..4af66b28f2
--- /dev/null
+++ b/packages/compartment-mapper/test/node-modules.test.js
@@ -0,0 +1,58 @@
+import 'ses';
+import fs from 'node:fs';
+import url from 'node:url';
+import test from 'ava';
+import { mapNodeModules } from '../src/node-modules.js';
+import { makeReadPowers } from '../src/node-powers.js';
+import { ANONYMOUS_COMPARTMENT } from '../src/node-modules.js';
+
+const { keys, entries, values } = Object;
+
+test('mapNodeModules() should fulfill with a denormalized CompartmentMapDescriptor', async t => {
+  t.plan(4);
+
+  const readPowers = makeReadPowers({ fs, url });
+  const moduleLocation = `${new URL(
+    'fixtures-0/node_modules/bundle/main.js',
+    import.meta.url,
+  )}`;
+
+  const { compartments, entry } = await mapNodeModules(
+    readPowers,
+    moduleLocation,
+  );
+
+  t.deepEqual(
+    values(compartments)
+      .map(({ name }) => name)
+      .sort(),
+    ['bundle', 'bundle-dep'],
+  );
+
+  t.true(keys(compartments).every(name => name.startsWith('file://')));
+
+  t.is(compartments[entry.compartment].name, 'bundle');
+
+  t.deepEqual(keys(compartments[entry.compartment].modules).sort(), [
+    '.',
+    'bundle',
+    'bundle-dep',
+  ]);
+});
+
+test(`mapNodeModules() should assign a package name when the entry point's package descriptor lacks a "name" field`, async t => {
+  t.plan(1);
+
+  const readPowers = makeReadPowers({ fs, url });
+  const moduleLocation = `${new URL(
+    'fixtures-anonymous/node_modules/unnamed/incognito/index.js',
+    import.meta.url,
+  )}`;
+
+  const { compartments } = await mapNodeModules(readPowers, moduleLocation);
+
+  t.deepEqual(
+    values(compartments).map(({ name }) => name),
+    [ANONYMOUS_COMPARTMENT],
+  );
+});