diff --git a/server/mergin/sync/config.py b/server/mergin/sync/config.py
index 5f91ce16..26a9d14c 100644
--- a/server/mergin/sync/config.py
+++ b/server/mergin/sync/config.py
@@ -62,3 +62,5 @@ class Configuration(object):
         "GEODIFF_WORKING_DIR",
         default=os.path.join(LOCAL_PROJECTS, "geodiff_tmp"),
     )
+    # in seconds, older unfinished zips are moved to temp
+    PARTIAL_ZIP_EXPIRATION = config("PARTIAL_ZIP_EXPIRATION", default=300, cast=int)
diff --git a/server/mergin/sync/private_api_controller.py b/server/mergin/sync/private_api_controller.py
index 9b93350c..e996fdfa 100644
--- a/server/mergin/sync/private_api_controller.py
+++ b/server/mergin/sync/private_api_controller.py
@@ -2,7 +2,7 @@
 #
 # SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-MerginMaps-Commercial
 import os
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from blinker import signal
 from connexion import NoContent
 from flask import (
@@ -45,7 +45,6 @@
 from .utils import get_x_accel_uri
 
 project_access_granted = signal("project_access_granted")
-PARTIAL_ZIP_EXPIRATION = 300  # seconds
 
 
 @auth_required
@@ -365,8 +364,8 @@ def download_project(id: str, version=None):  # noqa: E501 # pylint: disable=W06
     temp_zip_path = project_version.zip_path + ".partial"
     # to be safe we are not in vicious circle remove inactive partial zip
     if os.path.exists(temp_zip_path) and datetime.fromtimestamp(
-        os.path.getmtime(temp_zip_path)
-    ) < datetime.now(datetime.timezone.utc) - timedelta(
+        os.path.getmtime(temp_zip_path), tz=timezone.utc
+    ) < datetime.now(timezone.utc) - timedelta(
         seconds=current_app.config["PARTIAL_ZIP_EXPIRATION"]
     ):
         move_to_tmp(temp_zip_path)
diff --git a/server/mergin/tests/test_private_project_api.py b/server/mergin/tests/test_private_project_api.py
index 6e1906c8..0b72952c 100644
--- a/server/mergin/tests/test_private_project_api.py
+++ b/server/mergin/tests/test_private_project_api.py
@@ -473,3 +473,26 @@ def test_large_project_download_fail(client, diff_project):
     )
     assert resp.status_code == 400
     assert "The total size of requested files is too large" in resp.json["detail"]
+
+
+@patch("mergin.sync.tasks.create_project_version_zip.delay")
+def test_remove_abandoned_zip(mock_prepare_zip, client, diff_project):
+    """Test project download removes partial zip which is inactive for some time"""
+    latest_version = diff_project.get_latest_version()
+    # pretend an incomplete zip remained
+    partial_zip_path = latest_version.zip_path + ".partial"
+    os.makedirs(os.path.dirname(partial_zip_path), exist_ok=True)
+    os.mknod(partial_zip_path)
+    assert os.path.exists(partial_zip_path)
+    # pretend abandoned partial zip by lowering the expiration limit
+    client.application.config["PARTIAL_ZIP_EXPIRATION"] = 0
+    # download should remove it (move to temp folder) and call a celery task which will try to create a correct zip
+    resp = client.get(
+        url_for(
+            "/app.mergin_sync_private_api_controller_download_project",
+            id=diff_project.id,
+        )
+    )
+    assert mock_prepare_zip.called
+    assert resp.status_code == 202
+    assert not os.path.exists(partial_zip_path)