diff --git a/workspaces/arborist/lib/arborist/reify.js b/workspaces/arborist/lib/arborist/reify.js
index 6f1e2f402e55a..0c7b4fd0acfbf 100644
--- a/workspaces/arborist/lib/arborist/reify.js
+++ b/workspaces/arborist/lib/arborist/reify.js
@@ -90,7 +90,9 @@ module.exports = cls => class Reifier extends cls {
 
   // public method
   async reify (options = {}) {
-    const linked = (options.installStrategy || this.options.installStrategy) === 'linked'
+    // Global installs are normalized to the shallow strategy in the constructor; honor that here so a per-call installStrategy:'linked' can't re-engage the unsupported linked path.
+    const linked = !this.options.global &&
+      (options.installStrategy || this.options.installStrategy) === 'linked'
 
     if (this.options.packageLockOnly && this.options.global) {
       const er = new Error('cannot generate lockfile for global packages')
@@ -474,7 +476,10 @@ module.exports = cls => class Reifier extends cls {
       }
       if (includeRootDeps) {
         // add all non-workspace nodes to filterNodes
-        for (const tree of [this.idealTree, this.actualTree]) {
+        // Skip the actual tree under the linked diff wrapper: its edge targets have root===actualTree, not the wrapper, which trips Diff.calculate's filterNode guard.
+        // The ideal-side targets alone scope the diff.
+        const trees = this.#linkedActualForDiff ? [this.idealTree] : [this.idealTree, this.actualTree]
+        for (const tree of trees) {
           for (const { type, to } of tree.edgesOut.values()) {
             if (type !== 'workspace' && to) {
               filterNodes.push(to)
diff --git a/workspaces/arborist/test/arborist/reify.js b/workspaces/arborist/test/arborist/reify.js
index 08c2c2bde15be..42bd8f5941aa5 100644
--- a/workspaces/arborist/test/arborist/reify.js
+++ b/workspaces/arborist/test/arborist/reify.js
@@ -4514,6 +4514,64 @@ t.test('install strategy linked', async (t) => {
   })
 })
 
+t.test('linked strategy --workspaces=false and --include-workspace-root do not crash', async t => {
+  // Regression for #9614. Under linked, the root-dep filter nodes came from the real actual tree, not the synthesized diff wrapper, tripping Diff.calculate's "invalid filterNode" guard.
+  const manifest = deps => JSON.stringify({
+    name: 'root',
+    version: '1.0.0',
+    workspaces: ['packages/*'],
+    dependencies: deps,
+  })
+  const path = t.testdir({
+    'package.json': manifest({ abbrev: '1.1.1', wrappy: '1.0.2' }),
+    packages: {
+      a: {
+        'package.json': JSON.stringify({ name: 'a', version: '1.0.0' }),
+      },
+    },
+  })
+
+  createRegistry(t, true)
+  await reify(path, { installStrategy: 'linked' })
+
+  // --workspaces=false: only root deps are in scope.
+  await t.resolves(
+    reify(path, { installStrategy: 'linked', workspacesEnabled: false }),
+    '--workspaces=false does not crash'
+  )
+
+  // -w a --include-workspace-root: workspace a plus root deps in scope.
+  await t.resolves(
+    reify(path, { installStrategy: 'linked', workspaces: ['a'], includeWorkspaceRoot: true }),
+    '-w a --include-workspace-root does not crash'
+  )
+
+  t.ok(fs.lstatSync(resolve(path, 'node_modules/abbrev')).isSymbolicLink(), 'root dep still linked')
+
+  // Dropping the actual-side filter nodes must not stop a filtered install from pruning a removed root dep.
+  fs.writeFileSync(resolve(path, 'package.json'), manifest({ abbrev: '1.1.1' }))
+  await reify(path, { installStrategy: 'linked', workspacesEnabled: false })
+  t.notOk(fs.existsSync(resolve(path, 'node_modules/wrappy')), 'removed root dep pruned under filtered install')
+  t.ok(fs.lstatSync(resolve(path, 'node_modules/abbrev')).isSymbolicLink(), 'remaining root dep still linked')
+})
+
+t.test('global install ignores a per-call linked strategy', async t => {
+  // Regression for #9614. Global installs are normalized to shallow; a per-call installStrategy:'linked' must not re-engage the linked path, which would trip Diff.calculate's filterNode guard on re-install and delete the global package.
+  const path = t.testdir({ lib: {} })
+  const lib = resolve(path, 'lib')
+  const nm = resolve(lib, 'node_modules')
+
+  createRegistry(t, true)
+  await reify(lib, { add: ['abbrev@1.1.1'], global: true })
+
+  // Re-install the already-present package under linked: must not crash and must not remove it.
+  await t.resolves(
+    reify(lib, { add: ['abbrev@1.1.1'], global: true, installStrategy: 'linked' }),
+    'global re-install under linked does not crash'
+  )
+  t.strictSame(fs.readdirSync(nm), ['abbrev'], 'global package retained, no .store created')
+})
+
 t.test('linked strategy exposes store node_modules via NODE_PATH for lifecycle scripts', async t => {
   // Regression for #9549. In the linked strategy a store package's deps are symlinked siblings in its store node_modules.
   // A separate bin invoked by the script (e.g. napi-postinstall) resolves modules from its own store realpath and cannot see them, so npm exposes them via NODE_PATH.