diff --git a/.changeset/fix-workspace-state-race.md b/.changeset/fix-workspace-state-race.md
new file mode 100644
index 0000000000..e721c33043
--- /dev/null
+++ b/.changeset/fix-workspace-state-race.md
@@ -0,0 +1,6 @@
+---
+"@pnpm/workspace.state": patch
+"pnpm": patch
+---
+
+Avoid crashing when the workspace state cache is partially written or malformed.
diff --git a/pacquet/crates/workspace-state/Cargo.toml b/pacquet/crates/workspace-state/Cargo.toml
index e821e15963..f45369ad3c 100644
--- a/pacquet/crates/workspace-state/Cargo.toml
+++ b/pacquet/crates/workspace-state/Cargo.toml
@@ -17,10 +17,10 @@ derive_more = { workspace = true }
 indexmap    = { workspace = true }
 serde       = { workspace = true }
 serde_json  = { workspace = true }
+tempfile    = { workspace = true }
 
 [dev-dependencies]
 pretty_assertions = { workspace = true }
-tempfile          = { workspace = true }
 
 [lints]
 workspace = true
diff --git a/pacquet/crates/workspace-state/src/lib.rs b/pacquet/crates/workspace-state/src/lib.rs
index f84163fd7d..79892f9d5b 100644
--- a/pacquet/crates/workspace-state/src/lib.rs
+++ b/pacquet/crates/workspace-state/src/lib.rs
@@ -17,10 +17,12 @@ use pacquet_diagnostics::miette::{self, Diagnostic};
 use serde::{Deserialize, Serialize};
 use std::{
     collections::BTreeMap,
-    fs, io,
+    fs,
+    io::{self, Write},
     path::{Path, PathBuf},
     time::{SystemTime, UNIX_EPOCH},
 };
+use tempfile::NamedTempFile;
 
 /// Basename of the workspace-state file, written inside `node_modules/`.
 ///
@@ -177,10 +179,17 @@ pub enum UpdateWorkspaceStateError {
 
 /// Write `state` to `<workspace_dir>/node_modules/.pnpm-workspace-state-v1.json`.
 ///
-/// Mirrors upstream's [`updateWorkspaceState`](https://github.com/pnpm/pnpm/blob/7ff112bac6/workspace/state/src/updateWorkspaceState.ts):
-/// `JSON.stringify(state, undefined, 2) + '\n'`. `serde_json`'s pretty
-/// printer uses the same 2-space indent and `": "` separator as JS, so
-/// the on-disk bytes round-trip cleanly between the two writers.
+/// Writes to a temporary file in the same directory, then atomically
+/// renames it into place, so a concurrent reader — pnpm or pacquet —
+/// never observes a half-written file. Mirrors upstream's
+/// [`updateWorkspaceState`](https://github.com/pnpm/pnpm/blob/7ff112bac6/workspace/state/src/updateWorkspaceState.ts),
+/// which writes through `write-file-atomic` for the same reason
+/// ([#12020](https://github.com/pnpm/pnpm/issues/12020)).
+///
+/// The serialized bytes are `JSON.stringify(state, undefined, 2) + '\n'`:
+/// `serde_json`'s pretty printer uses the same 2-space indent and `": "`
+/// separator as JS, so the on-disk bytes round-trip cleanly between the
+/// two writers.
 pub fn update_workspace_state(
     workspace_dir: &Path,
     state: &WorkspaceState,
@@ -194,8 +203,17 @@ pub fn update_workspace_state(
     let mut serialized =
         serde_json::to_string_pretty(state).map_err(UpdateWorkspaceStateError::SerializeJson)?;
     serialized.push('\n');
-    fs::write(&file_path, serialized.as_bytes())
-        .map_err(|source| UpdateWorkspaceStateError::WriteFile { path: file_path, source })
+    let mut temp = NamedTempFile::new_in(parent).map_err(|source| {
+        UpdateWorkspaceStateError::WriteFile { path: file_path.clone(), source }
+    })?;
+    temp.write_all(serialized.as_bytes()).map_err(|source| {
+        UpdateWorkspaceStateError::WriteFile { path: file_path.clone(), source }
+    })?;
+    temp.persist(&file_path).map_err(|error| UpdateWorkspaceStateError::WriteFile {
+        path: file_path,
+        source: error.error,
+    })?;
+    Ok(())
 }
 
 /// Read the workspace state file at `<workspace_dir>/node_modules/.pnpm-workspace-state-v1.json`.
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 6839614edc..b46a022ca2 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -9957,6 +9957,9 @@ importers:
       ramda:
         specifier: 'catalog:'
         version: '@pnpm/ramda@0.28.1'
+      write-file-atomic:
+        specifier: 'catalog:'
+        version: 7.0.1
     devDependencies:
       '@jest/globals':
         specifier: 'catalog:'
@@ -9973,6 +9976,9 @@ importers:
       '@types/ramda':
         specifier: 'catalog:'
         version: 0.31.1
+      '@types/write-file-atomic':
+        specifier: 'catalog:'
+        version: 4.0.3
 
   workspace/workspace-manifest-reader:
     dependencies:
diff --git a/workspace/state/package.json b/workspace/state/package.json
index 5602fc14b4..9d06d3acec 100644
--- a/workspace/state/package.json
+++ b/workspace/state/package.json
@@ -35,7 +35,8 @@
     "@pnpm/catalogs.types": "workspace:*",
     "@pnpm/config.reader": "workspace:*",
     "@pnpm/types": "workspace:*",
-    "ramda": "catalog:"
+    "ramda": "catalog:",
+    "write-file-atomic": "catalog:"
   },
   "peerDependencies": {
     "@pnpm/logger": "catalog:"
@@ -45,7 +46,8 @@
     "@pnpm/logger": "workspace:*",
     "@pnpm/prepare": "workspace:*",
     "@pnpm/workspace.state": "workspace:*",
-    "@types/ramda": "catalog:"
+    "@types/ramda": "catalog:",
+    "@types/write-file-atomic": "catalog:"
   },
   "engines": {
     "node": ">=22.13"
diff --git a/workspace/state/src/loadWorkspaceState.ts b/workspace/state/src/loadWorkspaceState.ts
index 02176cdde2..98908e3dc5 100644
--- a/workspace/state/src/loadWorkspaceState.ts
+++ b/workspace/state/src/loadWorkspaceState.ts
@@ -18,5 +18,12 @@ export function loadWorkspaceState (workspaceDir: string): WorkspaceState | unde
     }
     throw error
   }
-  return JSON.parse(cacheFileContent) as WorkspaceState
+  try {
+    return JSON.parse(cacheFileContent) as WorkspaceState
+  } catch (error) {
+    if (util.types.isNativeError(error) && error.name === 'SyntaxError') {
+      return undefined
+    }
+    throw error
+  }
 }
diff --git a/workspace/state/src/updateWorkspaceState.ts b/workspace/state/src/updateWorkspaceState.ts
index a1aa8a71b0..164aab4751 100644
--- a/workspace/state/src/updateWorkspaceState.ts
+++ b/workspace/state/src/updateWorkspaceState.ts
@@ -3,6 +3,7 @@ import path from 'node:path'
 
 import { logger } from '@pnpm/logger'
 import type { ConfigDependencies } from '@pnpm/types'
+import writeFileAtomic from 'write-file-atomic'
 
 import { createWorkspaceState } from './createWorkspaceState.js'
 import { getFilePath } from './filePath.js'
@@ -23,5 +24,5 @@ export async function updateWorkspaceState (opts: UpdateWorkspaceStateOptions):
   const workspaceStateJSON = JSON.stringify(workspaceState, undefined, 2) + '\n'
   const cacheFile = getFilePath(opts.workspaceDir)
   await fs.promises.mkdir(path.dirname(cacheFile), { recursive: true })
-  await fs.promises.writeFile(cacheFile, workspaceStateJSON)
+  await writeFileAtomic(cacheFile, workspaceStateJSON)
 }
diff --git a/workspace/state/test/loadWorkspaceState.test.ts b/workspace/state/test/loadWorkspaceState.test.ts
index c1db7e850b..51ad4c3057 100644
--- a/workspace/state/test/loadWorkspaceState.test.ts
+++ b/workspace/state/test/loadWorkspaceState.test.ts
@@ -71,3 +71,15 @@ test('loadWorkspaceState() when cache file exists and is correct', async () => {
   expect(loadWorkspaceState(workspaceDir)).toStrictEqual(workspaceState)
   expect(jest.mocked(logger.debug).mock.calls).toStrictEqual(expectedLoggerCalls)
 })
+
+test('loadWorkspaceState() when cache file contains partial JSON', async () => {
+  prepareEmpty()
+
+  const workspaceDir = process.cwd()
+  const cacheFile = getFilePath(workspaceDir)
+  fs.mkdirSync(path.dirname(cacheFile), { recursive: true })
+  fs.writeFileSync(cacheFile, '{\n  "settings": ')
+
+  expect(loadWorkspaceState(workspaceDir)).toBeUndefined()
+  expect(jest.mocked(logger.debug).mock.calls).toStrictEqual(expectedLoggerCalls)
+})