diff --git a/lib/utils/installed-deep.js b/lib/utils/installed-deep.js
index 3c56c5d036f25..79fe9195a573f 100644
--- a/lib/utils/installed-deep.js
+++ b/lib/utils/installed-deep.js
@@ -21,9 +21,12 @@ const installedDeep = async (npm) => {
 
   const res = new Set()
   const gArb = new Arborist({
+    ...npm.flatOptions,
     global: true,
     path: resolve(npm.globalDir, '..'),
     workspacesEnabled,
+    // Completion only lists names; never execute a project .npm-extension.
+    ignoreExtension: true,
   })
   const gTree = await gArb.loadActual({ global: true })
 
@@ -32,7 +35,13 @@ const installedDeep = async (npm) => {
   }
 
   if (!global) {
-    const arb = new Arborist({ global: false, path: prefix, workspacesEnabled })
+    const arb = new Arborist({
+      ...npm.flatOptions,
+      global: false,
+      path: prefix,
+      workspacesEnabled,
+      ignoreExtension: true,
+    })
     const tree = await arb.loadActual()
     for (const node of getValues(tree)) {
       res.add(node.name)
diff --git a/test/lib/utils/installed-deep.js b/test/lib/utils/installed-deep.js
index 20e001aaec751..b32e71390809b 100644
--- a/test/lib/utils/installed-deep.js
+++ b/test/lib/utils/installed-deep.js
@@ -190,6 +190,28 @@ t.test('limit depth', async t => {
   )
 })
 
+t.test('does not execute .npm-extension during completion inventory', async t => {
+  const mock = await mockNpm(t, {
+    prefixDir: {
+      'package.json': JSON.stringify({
+        name: 'ext-poc',
+        version: '1.0.0',
+      }),
+      '.npm-extension.mjs': [
+        "throw new Error('npm-extension should not run during completion')",
+        'export const transformManifest = (pkg) => pkg',
+      ].join('\n'),
+    },
+    globalPrefixDir: globalFixture,
+    config: {
+      depth: Infinity,
+    },
+  })
+
+  const res = await installedDeep(mock.npm)
+  t.ok(Array.isArray(res), 'inventory still returns a list')
+})
+
 t.test('limit depth as global', async t => {
   const res = await mockDeep(t, { depth: 0, global: true })
   t.same(