diff --git a/src/utils/hash-utils.ts b/src/utils/hash-utils.ts
new file mode 100644
index 0000000..72a6b6f
--- /dev/null
+++ b/src/utils/hash-utils.ts
@@ -0,0 +1,7 @@
+import crypto from "crypto";
+import fs from "fs";
+
+export function computeHash(path: string, algorithm: string): Promise<crypto.Hash> {
+    const hash = crypto.createHash(algorithm);
+    return new Promise(resolve => fs.createReadStream(path).on("data", data => hash.update(data)).on("end", () => resolve(hash)));
+}
diff --git a/src/utils/modrinth-utils.ts b/src/utils/modrinth-utils.ts
index f2e9903..9af2d32 100644
--- a/src/utils/modrinth-utils.ts
+++ b/src/utils/modrinth-utils.ts
@@ -2,12 +2,13 @@ import { FormData } from "formdata-node";
 import { fileFromPath } from "formdata-node/file-from-path";
 import fetch from "node-fetch";
 import { File } from "./file";
+import { computeHash } from "./hash-utils";
 
-export async function createVersion(id: string, data: Record<string, any>, files: File[], token: string): Promise<string> {
+export async function createVersion(modId: string, data: Record<string, any>, files: File[], token: string): Promise<string> {
     data = {
         dependencies: [],
         ...data,
-        mod_id: id,
+        mod_id: modId,
         file_parts: files.map((_, i) => i.toString())
     };
 
@@ -32,5 +33,27 @@ export async function createVersion(id: string, data: Record<string, any>, files
         throw new Error(`Failed to upload file: ${response.status} (${errorText})`);
     }
 
-    return (<{ id: string }>await response.json()).id;
-}
\ No newline at end of file
+    const versionId = (<{ id: string }>await response.json()).id;
+    const primaryFile = files[0];
+    if (primaryFile) {
+        await makeFilePrimary(versionId, primaryFile.path, token);
+    }
+    return versionId;
+}
+
+export async function makeFilePrimary(versionId: string, filePath: string, token: string): Promise<boolean> {
+    const algorithm = "sha1";
+    const hash = (await computeHash(filePath, algorithm)).digest("hex");
+
+    const response = await fetch(`https://api.modrinth.com/api/v1/version/${versionId}`, {
+        method: "PATCH",
+        headers: {
+            "Authorization": token,
+            "Content-Type": "application/json"
+        },
+        body: JSON.stringify({
+            primary_file: [algorithm, hash]
+        })
+    });
+    return response.ok;
+}
diff --git a/test/hast-utils.test.ts b/test/hast-utils.test.ts
new file mode 100644
index 0000000..e733af0
--- /dev/null
+++ b/test/hast-utils.test.ts
@@ -0,0 +1,22 @@
+import { describe, test, expect } from "@jest/globals";
+import { computeHash } from "../src/utils/hash-utils";
+
+describe("computeHash", () => {
+    test("sha1 is supported", async () => {
+        const algorithm = "sha1";
+        expect((await computeHash("./test/content/fabric.mod.json", algorithm)).digest("hex")).toBe("be90f16aa5c806e2bbcf151efee4ebce7899256b");
+        expect((await computeHash("./test/content/mods.toml", algorithm)).digest("hex")).toBe("bf13f9ca36d5a5ebd55a3bda0b432ab4a007791a");
+    });
+
+    test("sha256 is supported", async () => {
+        const algorithm = "sha256";
+        expect((await computeHash("./test/content/fabric.mod.json", algorithm)).digest("hex")).toBe("583334cd90510cdc5c5068dd7cc3423adc9674abf8e200b3a165216bb0f6346d");
+        expect((await computeHash("./test/content/mods.toml", algorithm)).digest("hex")).toBe("c420fd754f32553dde2a5118c27ca83b644ba73d230baf723fa00d5cb5b1aaac");
+    });
+
+    test("sha512 is supported", async () => {
+        const algorithm = "sha512";
+        expect((await computeHash("./test/content/fabric.mod.json", algorithm)).digest("hex")).toBe("18582ba1fbec5ab05d5b5679f6d5fa157792959fd22ac091f1be264fc709996d900c8514265f0d24e533c1174da2919fdd7441d1215bbf6866e68f71114979af");
+        expect((await computeHash("./test/content/mods.toml", algorithm)).digest("hex")).toBe("b15c84290a1f9fad17fa4f3429fbb67d2555feafd617a5399ba95d5b6745659bc50e16e810d3bfe5bbdd4b66720b85daafd5ad78ece9a484c356c358d7b295ec");
+    });
+});