diff --git a/.changeset/famous-cloths-press.md b/.changeset/famous-cloths-press.md
new file mode 100644
index 0000000000..4ee116265c
--- /dev/null
+++ b/.changeset/famous-cloths-press.md
@@ -0,0 +1,6 @@
+---
+"@pnpm/reviewing.dependencies-hierarchy": patch
+"pnpm": patch
+---
+
+Handle undefined pkgSnapshot in `pnpm why -r` [#10700](https://github.com/pnpm/pnpm/issues/10700).
diff --git a/reviewing/dependencies-hierarchy/src/getPkgInfo.ts b/reviewing/dependencies-hierarchy/src/getPkgInfo.ts
index 16b062b06f..f2f999a310 100644
--- a/reviewing/dependencies-hierarchy/src/getPkgInfo.ts
+++ b/reviewing/dependencies-hierarchy/src/getPkgInfo.ts
@@ -68,7 +68,7 @@ export function getPkgInfo (opts: GetPkgInfoOpts): { pkgInfo: PackageInfo, readM
   let integrity: string | undefined
   const depPath = refToRelative(opts.ref, opts.alias)
   if (depPath) {
-    let pkgSnapshot!: PackageSnapshot
+    let pkgSnapshot: PackageSnapshot | undefined
     if (opts.currentPackages[depPath]) {
       pkgSnapshot = opts.currentPackages[depPath]
       const parsed = nameVerFromPkgSnapshot(depPath, pkgSnapshot)
@@ -87,12 +87,14 @@ export function getPkgInfo (opts: GetPkgInfoOpts): { pkgInfo: PackageInfo, readM
       isMissing = true
       isSkipped = opts.skipped.has(depPath)
     }
-    resolved = (pkgSnapshotToResolution(depPath, pkgSnapshot, opts.registries) as TarballResolution).tarball
-    depType = opts.depTypes[depPath]
-    optional = pkgSnapshot.optional
-    if ('integrity' in pkgSnapshot.resolution) {
-      integrity = pkgSnapshot.resolution.integrity as string
+    if (pkgSnapshot) {
+      resolved = (pkgSnapshotToResolution(depPath, pkgSnapshot, opts.registries) as TarballResolution).tarball
+      optional = pkgSnapshot.optional
+      if ('integrity' in pkgSnapshot.resolution) {
+        integrity = pkgSnapshot.resolution.integrity as string
+      }
     }
+    depType = opts.depTypes[depPath]
   } else {
     name = opts.alias
     version = opts.ref
diff --git a/reviewing/dependencies-hierarchy/test/getPkgInfo.test.ts b/reviewing/dependencies-hierarchy/test/getPkgInfo.test.ts
new file mode 100644
index 0000000000..cf79a4e087
--- /dev/null
+++ b/reviewing/dependencies-hierarchy/test/getPkgInfo.test.ts
@@ -0,0 +1,33 @@
+import { getPkgInfo, type GetPkgInfoOpts } from '../src/getPkgInfo.js'
+import path from 'path'
+
+test('getPkgInfo handles missing pkgSnapshot without crashing', () => {
+  const opts: GetPkgInfoOpts = {
+    alias: 'missing-pkg',
+    ref: 'missing-pkg@1.0.0',
+    currentPackages: {},
+    wantedPackages: {},
+    depTypes: {},
+    skipped: new Set<string>(),
+    registries: {
+      default: 'https://registry.npmjs.org/',
+    },
+    virtualStoreDirMaxLength: 120,
+    modulesDir: '',
+    linkedPathBaseDir: '',
+  }
+
+  const result = getPkgInfo(opts)
+
+  expect(result.pkgInfo).toEqual({
+    alias: 'missing-pkg',
+    name: 'missing-pkg',
+    version: 'missing-pkg@1.0.0',
+    isMissing: true,
+    isPeer: false,
+    isSkipped: false,
+    path: path.join('.pnpm/missing-pkg@1.0.0/node_modules/missing-pkg'),
+  })
+  expect(result.pkgInfo.resolved).toBeUndefined()
+  expect(result.pkgInfo.optional).toBeUndefined()
+})