diff --git a/.changeset/upload-blob-metadata.md b/.changeset/upload-blob-metadata.md
new file mode 100644
index 000000000..3e2532125
--- /dev/null
+++ b/.changeset/upload-blob-metadata.md
@@ -0,0 +1,5 @@
+---
+"@solidjs/start": patch
+---
+
+Keep the metadata of files and blobs sent to server functions. A blob arrives as a `Blob` instead of a `File` named `blob`, an empty type stays empty instead of `application/octet-stream`, and a file keeps its exact name and its `lastModified`. The server still reads uploads from clients that send only the part index.
diff --git a/packages/start/src/runtime/uploads.test.ts b/packages/start/src/runtime/uploads.test.ts
index e8c85c475..e235716e4 100644
--- a/packages/start/src/runtime/uploads.test.ts
+++ b/packages/start/src/runtime/uploads.test.ts
@@ -1,3 +1,4 @@
+import { createPlugin, type SerovalNode } from "seroval";
 import { createApp, toWebHandler } from "vinxi/http";
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import { serializeToJSONString } from "./serialization";
@@ -95,6 +96,59 @@ describe("server function uploads", () => {
     expect((second as { again: File }).again).toBe(first);
   });
 
+  it("keeps the type of a blob", async () => {
+    const [received] = await roundTrip(new Blob(["{}"], { type: "application/json" }));
+
+    expect(received).toBeInstanceOf(Blob);
+    expect((received as Blob).type).toBe("application/json");
+    expect(await (received as Blob).text()).toBe("{}");
+  });
+
+  it("keeps a blob a blob, with its empty type", async () => {
+    const [received] = await roundTrip(new Blob(["raw"]));
+
+    // Every part arrives as a file, and an empty type as application/octet-stream.
+    expect(received).toBeInstanceOf(Blob);
+    expect(received).not.toBeInstanceOf(File);
+    expect((received as Blob).type).toBe("");
+    expect(await (received as Blob).text()).toBe("raw");
+  });
+
+  it("keeps the name and lastModified of a file", async () => {
+    // The form encoder escapes a quote as %22, and the parser decodes every %22.
+    const file = new File(["x"], 'a"b%22.txt', { type: "text/plain", lastModified: 1234 });
+
+    const [received] = await roundTrip(file);
+
+    expect((received as File).name).toBe('a"b%22.txt');
+    expect((received as File).lastModified).toBe(1234);
+  });
+
+  it("reads an upload from a client that sends only the index", async () => {
+    // The plugin of clients before the metadata fields.
+    const legacy = createPlugin<Blob, { i: SerovalNode }>({
+      tag: "solid-start/upload",
+      test: value => value instanceof Blob,
+      parse: {
+        sync: (_value, ctx) => ({ i: ctx.parse(0) }),
+        async: async (_value, ctx) => ({ i: await ctx.parse(0) }),
+        stream: (_value, ctx) => ({ i: ctx.parse(0) })
+      },
+      serialize: () => "",
+      deserialize: () => {
+        throw new Error("unused");
+      }
+    });
+    const form = new FormData();
+    form.set(ARGS_PART, await serializeToJSONString([new File(["x"], "x.txt")], [legacy]));
+    form.set(`${FILE_PART}0`, new File(["x"], "x.txt"));
+
+    const [received] = (await readUploadArgs(form)) as [File];
+
+    expect(received.name).toBe("x.txt");
+    expect(await received.text()).toBe("x");
+  });
+
   it("copies a blob from another frame", async () => {
     const source = new Blob(["other"], { type: "text/plain" });
     // Not an instance of this realm's Blob, as one from another frame isn't.
diff --git a/packages/start/src/runtime/uploads.ts b/packages/start/src/runtime/uploads.ts
index 65dc2f5e6..73588facc 100644
--- a/packages/start/src/runtime/uploads.ts
+++ b/packages/start/src/runtime/uploads.ts
@@ -47,7 +47,14 @@ const UPLOAD_TAG = "solid-start/upload";
  * bodies for a while, because an open tab can call a newer server.
  */
 
-type UploadNode = { i: SerovalNode };
+/**
+ * The index of the part, and what a multipart part does not keep: the type
+ * (an empty one arrives as `application/octet-stream`), whether the value was
+ * a blob or a file (every part arrives as a file), and the file's name (some
+ * characters are escaped) and `lastModified`. Clients before these fields
+ * send only the index.
+ */
+type UploadNode = { i: SerovalNode; t?: SerovalNode; n?: SerovalNode; l?: SerovalNode };
 
 /**
  * True for a file or a blob. One from another frame is an instance of that
@@ -70,20 +77,43 @@ function malformed(): Error {
   return new Error("Malformed server function upload.");
 }
 
+function isFile(value: Blob): value is File {
+  const file = value as Partial<File>;
+  return typeof file.name === "string" && typeof file.lastModified === "number";
+}
+
 /**
  * Serializes each file or blob in the arguments as its index in `files`, so
  * the call can send it as a form part. Seroval calls this wherever it finds
  * one: in arrays, objects, maps, sets and form data.
  */
 export function createUploadSerializer(files: Blob[]): Plugin<Blob, UploadNode> {
-  const parse = (value: Blob) => files.push(value) - 1;
+  // The fields are plain values, so the sync parser works for every mode.
+  const parse = (value: Blob, ctx: { parse(value: unknown): SerovalNode }): UploadNode => {
+    const node: UploadNode = { i: ctx.parse(files.push(value) - 1), t: ctx.parse(value.type) };
+    if (isFile(value)) {
+      node.n = ctx.parse(value.name);
+      node.l = ctx.parse(value.lastModified);
+    }
+    return node;
+  };
   return createPlugin<Blob, UploadNode>({
     tag: UPLOAD_TAG,
     test: isBlob,
     parse: {
-      sync: (value, ctx) => ({ i: ctx.parse(parse(value)) }),
-      async: async (value, ctx) => ({ i: await ctx.parse(parse(value)) }),
-      stream: (value, ctx) => ({ i: ctx.parse(parse(value)) })
+      sync: parse,
+      async: async (value, ctx) => {
+        const node: UploadNode = {
+          i: await ctx.parse(files.push(value) - 1),
+          t: await ctx.parse(value.type)
+        };
+        if (isFile(value)) {
+          node.n = await ctx.parse(value.name);
+          node.l = await ctx.parse(value.lastModified);
+        }
+        return node;
+      },
+      stream: parse
     },
     serialize: (node, ctx) => ctx.serialize(node.i),
     deserialize: () => {
@@ -122,7 +152,16 @@ export function createUploadDeserializer(form: FormData): Plugin<Blob, UploadNod
       }
       const part = form.get(`${FILE_PART}${index}`);
       if (!(part instanceof Blob)) throw malformed();
-      return part;
+      // A client before the metadata fields sends only the index.
+      if (node.t === undefined) return part;
+      const type = ctx.deserialize(node.t);
+      if (typeof type !== "string") throw malformed();
+      // The new blob or file refers to the bytes of the part instead of copying them.
+      if (node.n === undefined) return new Blob([part], { type });
+      const name = ctx.deserialize(node.n);
+      const lastModified = node.l === undefined ? undefined : ctx.deserialize(node.l);
+      if (typeof name !== "string" || typeof lastModified !== "number") throw malformed();
+      return new File([part], name, { type, lastModified });
     }
   });
 }