diff --git a/subiquity/models/filesystem.py b/subiquity/models/filesystem.py
index 66409b1a..1e1fa7e6 100644
--- a/subiquity/models/filesystem.py
+++ b/subiquity/models/filesystem.py
@@ -36,6 +36,7 @@ from curtin.util import human2bytes
 from probert.storage import StorageInfo
 
 from subiquity.common.types import Bootloader, OsProber, RecoveryKey
+from subiquitycore.utils import write_named_tempfile
 
 log = logging.getLogger("subiquity.models.filesystem")
 
@@ -1135,10 +1136,7 @@ class DM_Crypt(_Formattable):
 
     def serialize_key(self):
         if self.key and not self.keyfile:
-            f = tempfile.NamedTemporaryFile(prefix="luks-key-", mode="w", delete=False)
-            f.write(self.key)
-            f.close()
-            return {"keyfile": f.name}
+            return {"keyfile": write_named_tempfile("luks-key-", self.key)}
         else:
             return {}
 
diff --git a/subiquitycore/utils.py b/subiquitycore/utils.py
index 2a283b5f..89ef1742 100644
--- a/subiquitycore/utils.py
+++ b/subiquitycore/utils.py
@@ -19,6 +19,7 @@ import logging
 import os
 import random
 import subprocess
+import tempfile
 from typing import Any, Dict, List, Sequence
 
 log = logging.getLogger("subiquitycore.utils")
@@ -282,3 +283,10 @@ def gen_zsys_uuid():
     """Create a 6 character identifier.  Functionally equivalent to
     `head -100 /dev/urandom | tr -dc 'a-z0-9' | head -c6`"""
     return "".join([random.choice(_zsys_uuid_charset()) for i in range(6)])
+
+
+def write_named_tempfile(prefix, contents):
+    f = tempfile.NamedTemporaryFile(prefix=prefix, mode="w", delete=False)
+    with f:
+        f.write(contents)
+    return f.name