diff --git a/opensafely/jobrunner/executors/volumes.py b/opensafely/jobrunner/executors/volumes.py
index aef99d5b..8d053db1 100644
--- a/opensafely/jobrunner/executors/volumes.py
+++ b/opensafely/jobrunner/executors/volumes.py
@@ -1,5 +1,6 @@
 import importlib
 import logging
+import os
 import shutil
 import sys
 import tempfile
@@ -57,10 +58,20 @@ def delete_volume(job):
         docker.delete_volume(docker_volume_name(job))
 
     def write_timestamp(job, path, timeout=None):
-        with tempfile.NamedTemporaryFile() as f:
+        try:
+            # Note: writing to the temporary file while there's already a handle open to it
+            # is fine on unix, but sometimes errors on Windows, so we can't use a context
+            # manager for opening and writing to the temp file here.
+            f = tempfile.NamedTemporaryFile(delete=False)  # noqa: SIM115
+            f.close()
             p = Path(f.name)
             p.write_text(str(time.time_ns()))
             docker.copy_to_volume(docker_volume_name(job), p, path, timeout)
+        finally:
+            try:
+                os.remove(f.name)
+            except Exception:  # noqa: S110 (ruff wants us to log this)
+                pass
 
     def read_timestamp(job, path, timeout=None):
         return docker.read_timestamp(docker_volume_name(job), path, timeout)