diff --git a/nix_update/update.py b/nix_update/update.py
index f4e64cd..073a2f6 100644
--- a/nix_update/update.py
+++ b/nix_update/update.py
@@ -1,6 +1,7 @@
 import fileinput
-from typing import List
+from typing import List, Optional, Dict
 import subprocess
+import tempfile
 
 from .errors import UpdateError
 from .eval import Package, eval_attr
@@ -66,7 +67,16 @@ def replace_hash(filename: str, current: str, target: str) -> None:
 
 
 def nix_prefetch(cmd: List[str]) -> str:
-    res = run(["nix-prefetch"] + cmd)
+    extra_env: Dict[str, str] = {}
+    tempdir: Optional[tempfile.TemporaryDirectory[str]] = None
+    if extra_env.get("XDG_RUNTIME_DIR") is None:
+        tempdir = tempfile.TemporaryDirectory()
+        extra_env["XDG_RUNTIME_DIR"] = tempdir.name
+    try:
+        res = run(["nix-prefetch"] + cmd, extra_env=extra_env)
+    finally:
+        if tempdir:
+            tempdir.cleanup()
     return res.stdout.strip()
 
 
diff --git a/nix_update/utils.py b/nix_update/utils.py
index 6a74da0..4a734d3 100644
--- a/nix_update/utils.py
+++ b/nix_update/utils.py
@@ -3,7 +3,7 @@
 import subprocess
 import sys
 from pathlib import Path
-from typing import IO, Any, Callable, List, Optional, Union
+from typing import IO, Any, Callable, List, Optional, Union, Dict
 
 HAS_TTY = sys.stdout.isatty()
 ROOT = Path(os.path.dirname(os.path.realpath(__file__)))
@@ -28,9 +28,14 @@ def run(
     cwd: Optional[Union[Path, str]] = None,
     stdout: Union[None, int, IO[Any]] = subprocess.PIPE,
     check: bool = True,
+    extra_env: Dict[str, str] = {},
 ) -> "subprocess.CompletedProcess[str]":
     info("$ " + " ".join(command))
-    return subprocess.run(command, cwd=cwd, check=check, text=True, stdout=stdout)
+    env = os.environ.copy()
+    env.update(extra_env)
+    return subprocess.run(
+        command, cwd=cwd, check=check, text=True, stdout=stdout, env=env
+    )
 
 
 def extract_version(version: str, version_regex: str) -> Optional[str]: