diff --git a/nix-js/runtime-ts/src/builtins/io.ts b/nix-js/runtime-ts/src/builtins/io.ts
index 176558b..ca2433c 100644
--- a/nix-js/runtime-ts/src/builtins/io.ts
+++ b/nix-js/runtime-ts/src/builtins/io.ts
@@ -87,18 +87,17 @@ export const fetchClosure = (args: NixValue): never => {
   throw new Error("Not implemented: fetchClosure");
 };
 
-interface FetchUrlResult {
+export interface FetchUrlResult {
   store_path: string;
   hash: string;
 }
 
-interface FetchTarballResult {
+export interface FetchTarballResult {
   store_path: string;
-  hash: string;
   nar_hash: string;
 }
 
-interface FetchGitResult {
+export interface FetchGitResult {
   out_path: string;
   rev: string;
   short_rev: string;
@@ -109,7 +108,7 @@ interface FetchGitResult {
   nar_hash: string | null;
 }
 
-interface FetchHgResult {
+export interface FetchHgResult {
   out_path: string;
   branch: string;
   rev: string;
@@ -137,16 +136,11 @@ const normalizeUrlInput = (
   return { url, hash, name, executable };
 };
 
-const normalizeTarballInput = (
-  args: NixValue,
-): { url: string; sha256?: string; name?: string } => {
+const normalizeTarballInput = (args: NixValue): { url: string; sha256?: string; name?: string } => {
   const forced = force(args);
   if (isAttrs(forced)) {
     const url = forceStringNoCtx(forced.url);
-    const sha256 =
-      "sha256" in forced
-        ? forceStringNoCtx(forced.sha256)
-        : undefined;
+    const sha256 = "sha256" in forced ? forceStringNoCtx(forced.sha256) : undefined;
     const name = "name" in forced ? forceStringNoCtx(forced.name) : undefined;
     return { url, sha256, name };
   } else {
@@ -167,11 +161,7 @@ export const fetchurl = (args: NixValue): string => {
 
 export const fetchTarball = (args: NixValue): string => {
   const { url, name, sha256 } = normalizeTarballInput(args);
-  const result: FetchTarballResult = Deno.core.ops.op_fetch_tarball(
-    url,
-    name ?? null,
-    sha256 ?? null,
-  );
+  const result: FetchTarballResult = Deno.core.ops.op_fetch_tarball(url, name ?? null, sha256 ?? null);
   return result.store_path;
 };
 
diff --git a/nix-js/runtime-ts/src/types/global.d.ts b/nix-js/runtime-ts/src/types/global.d.ts
index 2faa4af..72fb844 100644
--- a/nix-js/runtime-ts/src/types/global.d.ts
+++ b/nix-js/runtime-ts/src/types/global.d.ts
@@ -1,34 +1,5 @@
 import type { NixRuntime } from "..";
-
-interface FetchUrlResult {
-  store_path: string;
-  hash: string;
-}
-
-interface FetchTarballResult {
-  store_path: string;
-  hash: string;
-  nar_hash: string;
-}
-
-interface FetchGitResult {
-  out_path: string;
-  rev: string;
-  short_rev: string;
-  rev_count: number;
-  last_modified: number;
-  last_modified_date: string;
-  submodules: boolean;
-  nar_hash: string | null;
-}
-
-interface FetchHgResult {
-  out_path: string;
-  branch: string;
-  rev: string;
-  short_rev: string;
-  rev_count: number;
-}
+import type { FetchTarballResult, FetchUrlResult, FetchGitResult, FetchHgResult } from "../builtins/io";
 
 declare global {
   var Nix: NixRuntime;
diff --git a/nix-js/src/fetcher.rs b/nix-js/src/fetcher.rs
index 4203bbe..5d2cded 100644
--- a/nix-js/src/fetcher.rs
+++ b/nix-js/src/fetcher.rs
@@ -32,7 +32,6 @@ pub struct FetchUrlResult {
 #[derive(Serialize)]
 pub struct FetchTarballResult {
     pub store_path: String,
-    pub hash: String,
     pub nar_hash: String,
 }
 
@@ -202,18 +201,12 @@ pub fn op_fetch_tarball<Ctx: RuntimeContext>(
             .get("nar_hash")
             .and_then(|v| v.as_str())
             .unwrap_or("");
-        let cached_tarball_hash = cached_entry
-            .info
-            .get("tarball_hash")
-            .and_then(|v| v.as_str())
-            .unwrap_or("");
 
         if let Some(ref hex) = expected_hex {
             if cached_nar_hash == hex {
                 info!("Cache hit");
                 return Ok(FetchTarballResult {
                     store_path: cached_entry.store_path.clone(),
-                    hash: cached_tarball_hash.to_string(),
                     nar_hash: cached_nar_hash.to_string(),
                 });
             }
@@ -221,7 +214,6 @@ pub fn op_fetch_tarball<Ctx: RuntimeContext>(
             info!("Cache hit (no hash check)");
             return Ok(FetchTarballResult {
                 store_path: cached_entry.store_path.clone(),
-                hash: cached_tarball_hash.to_string(),
                 nar_hash: cached_nar_hash.to_string(),
             });
         }
@@ -235,17 +227,6 @@ pub fn op_fetch_tarball<Ctx: RuntimeContext>(
 
     info!(bytes = data.len(), "Download complete");
 
-    let tarball_hash = crate::nix_utils::sha256_hex(&String::from_utf8_lossy(&data));
-
-    if let Some(ref expected) = expected_hex
-        && tarball_hash != *expected
-    {
-        return Err(NixRuntimeError::from(format!(
-            "Tarball hash mismatch for '{}': expected {}, got {}",
-            url, expected, tarball_hash
-        )));
-    }
-
     info!("Extracting tarball");
     let cache = FetcherCache::new().map_err(|e| NixRuntimeError::from(e.to_string()))?;
     let (extracted_path, _temp_dir) = cache
@@ -258,19 +239,16 @@ pub fn op_fetch_tarball<Ctx: RuntimeContext>(
     let nar_hash_hex = hex::encode(nar_hash);
 
     debug!(
-        tarball_hash = %tarball_hash,
         nar_hash = %nar_hash_hex,
         "Hash computation complete"
     );
 
-    if let Some(ref expected) = expected_sha256
-        && nar_hash != *expected
+    if let Some(ref expected) = expected_hex
+        && nar_hash_hex != *expected
     {
         return Err(NixRuntimeError::from(format!(
-            "NAR hash mismatch for '{}': expected {}, got {}",
-            url,
-            expected_hex.expect("must be Some"),
-            nar_hash_hex
+            "Tarball hash mismatch for '{}': expected {}, got {}",
+            url, expected, nar_hash_hex
         )));
     }
 
@@ -284,8 +262,7 @@ pub fn op_fetch_tarball<Ctx: RuntimeContext>(
     info!(store_path = %store_path, "Added to store");
 
     let info = serde_json::json!({
-        "tarball_hash": tarball_hash,
-        "nar_hash": nar_hash,
+        "nar_hash": nar_hash_hex,
         "url": url,
     });
 
@@ -296,7 +273,6 @@ pub fn op_fetch_tarball<Ctx: RuntimeContext>(
 
     Ok(FetchTarballResult {
         store_path,
-        hash: tarball_hash,
         nar_hash: nar_hash_hex,
     })
 }