diff --git a/packages/server/src/server/file-upload/index.test.ts b/packages/server/src/server/file-upload/index.test.ts
index 7eb97a07c3..8761529ec6 100644
--- a/packages/server/src/server/file-upload/index.test.ts
+++ b/packages/server/src/server/file-upload/index.test.ts
@@ -1,6 +1,6 @@
 import { existsSync, mkdtempSync, readFileSync, readdirSync, realpathSync, rmSync } from "node:fs";
 import { tmpdir } from "node:os";
-import { dirname, join } from "node:path";
+import { basename, dirname, join } from "node:path";
 import { afterEach, describe, expect, it, vi } from "vitest";
 
 import {
@@ -56,6 +56,49 @@ describe("file uploads", () => {
     expect(readFileSync(path, "utf8")).toBe("hello world");
   });
 
+  it("keeps the original file name for non-ASCII and punctuated names", async () => {
+    const uploads = new FileUploadStore({ paseoHome: makePaseoHome() });
+
+    for (const fileName of [
+      "2026年9月绩效计划表.xlsx",
+      "테스트 파일 (1).xlsx",
+      "résumé [final] & notes, v2.pdf",
+      "cafe\u0301 हिंदी.txt",
+    ]) {
+      const file = await uploadNamed(uploads, fileName);
+      expect(file?.fileName).toBe(fileName);
+      expect(basename(file!.path)).toBe(fileName);
+      expect(readFileSync(file!.path, "utf8")).toBe("hello world");
+    }
+  });
+
+  it("replaces path separators, control characters, and characters Windows rejects", async () => {
+    const uploads = new FileUploadStore({ paseoHome: makePaseoHome() });
+
+    await expect(uploadNamed(uploads, "../../etc/passwd")).resolves.toMatchObject({
+      fileName: "passwd",
+    });
+    const backslashed = await uploadNamed(uploads, "dir\\name.txt");
+    expect(backslashed?.fileName).not.toContain("\\");
+    expect(backslashed?.fileName).toMatch(/name\.txt$/);
+    await expect(uploadNamed(uploads, 'a<b>:"c|?*.txt')).resolves.toMatchObject({
+      fileName: "a_b___c___.txt",
+    });
+    await expect(uploadNamed(uploads, "line\nbreak.txt")).resolves.toMatchObject({
+      fileName: "line_break.txt",
+    });
+  });
+
+  it("shortens a long non-ASCII name to the file system limit and keeps its extension", async () => {
+    const uploads = new FileUploadStore({ paseoHome: makePaseoHome() });
+
+    const file = await uploadNamed(uploads, `${"绩".repeat(100)}.xlsx`);
+
+    expect(file?.fileName).toBe(`${"绩".repeat(83)}.xlsx`);
+    expect(Buffer.byteLength(file!.fileName)).toBeLessThanOrEqual(255);
+    expect(readFileSync(file!.path, "utf8")).toBe("hello world");
+  });
+
   it("rejects chunks beyond the declared size and removes the partial file", async () => {
     const paseoHome = makePaseoHome();
     const uploads = new FileUploadStore({ paseoHome });
@@ -202,6 +245,25 @@ describe("file uploads", () => {
   });
 });
 
+let uploadCount = 0;
+
+async function uploadNamed(uploads: FileUploadStore, fileName: string) {
+  const requestId = `req-named-${uploadCount++}`;
+  uploads.beginUpload({
+    type: "file.upload.request",
+    fileName,
+    mimeType: "text/plain",
+    size: 11,
+    modifiedAt: "2026-05-02T00:00:00.000Z",
+    requestId,
+  });
+  await uploads.receiveFrame(uploadBegins(requestId));
+  await uploads.receiveFrame(uploadChunk(requestId, "hello world"));
+  const response = await uploads.receiveFrame(uploadEnds(requestId));
+  expect(response?.payload.error).toBeNull();
+  return response?.payload.file;
+}
+
 function makePaseoHome(): string {
   const root = realpathSync(mkdtempSync(join(tmpdir(), "file-upload-test-")));
   tempDirs.push(root);
diff --git a/packages/server/src/server/file-upload/index.ts b/packages/server/src/server/file-upload/index.ts
index 8b93e31f2f..979130d875 100644
--- a/packages/server/src/server/file-upload/index.ts
+++ b/packages/server/src/server/file-upload/index.ts
@@ -1,6 +1,6 @@
 import { randomUUID } from "node:crypto";
 import { appendFile, mkdir, rm, writeFile } from "node:fs/promises";
-import { basename, join } from "node:path";
+import { basename, extname, join } from "node:path";
 
 import { FileTransferOpcode, type FileTransferFrame } from "@getpaseo/protocol/binary-frames/index";
 import { getErrorMessage } from "@getpaseo/protocol/error-utils";
@@ -220,9 +220,26 @@ function buildUploadResponse(upload: PendingUpload, error: string | null): FileU
   };
 }
 
+// Most file systems cap a single file name at 255 bytes.
+const MAX_FILE_NAME_BYTES = 255;
+
+// Keeps the client's file name, replacing only what cannot appear in a single
+// file name on Linux, macOS, or Windows.
 function sanitizeFileName(value: string): string {
   const name = basename(value)
-    .replace(/[^a-zA-Z0-9._ -]/g, "_")
+    .replace(/[\p{Cc}\\/:*?"<>|]/gu, "_")
     .trim();
-  return name.length > 0 && name !== "." && name !== ".." ? name : "upload";
+  return fitFileNameLength(name.length > 0 && name !== "." && name !== ".." ? name : "upload");
+}
+
+function fitFileNameLength(name: string): string {
+  if (Buffer.byteLength(name) <= MAX_FILE_NAME_BYTES) return name;
+  const extension = extname(name);
+  const keptExtension = Buffer.byteLength(extension) < MAX_FILE_NAME_BYTES ? extension : "";
+  let stem = "";
+  for (const char of name.slice(0, name.length - keptExtension.length)) {
+    if (Buffer.byteLength(stem + char + keptExtension) > MAX_FILE_NAME_BYTES) break;
+    stem += char;
+  }
+  return stem + keptExtension;
 }