diff --git a/fdroidserver/scanner.py b/fdroidserver/scanner.py
index 94eddcc0..ee26fce4 100644
--- a/fdroidserver/scanner.py
+++ b/fdroidserver/scanner.py
@@ -354,6 +354,8 @@ class SUSSDataController(SignatureDataController):
 
 
 class ScannerTool:
+    refresh_allowed = True
+
     def __init__(self):
         # we could add support for loading additional signature source
         # definitions from config.yml here
@@ -362,7 +364,9 @@ class ScannerTool:
 
         options = common.get_options()
         options_refresh_scanner = (
-            hasattr(options, "refresh_scanner") and options.refresh_scanner
+            hasattr(options, "refresh_scanner")
+            and options.refresh_scanner
+            and ScannerTool.refresh_allowed
         )
         if options_refresh_scanner or common.get_config().get('refresh_scanner'):
             self.refresh()
diff --git a/tests/scanner.TestCase b/tests/scanner.TestCase
index 3127f023..9d0440c0 100755
--- a/tests/scanner.TestCase
+++ b/tests/scanner.TestCase
@@ -33,6 +33,11 @@ import fdroidserver.scanner
 from testcommon import TmpCwd, mkdtemp, mock_open_to_str, parse_args_for_test
 
 
+# Always use built-in default rules so changes in downloaded rules don't break tests.
+@mock.patch(
+    'fdroidserver.scanner.SUSSDataController.load',
+    fdroidserver.scanner.SUSSDataController.load_from_defaults,
+)
 class ScannerTest(unittest.TestCase):
     def setUp(self):
         logging.basicConfig(level=logging.INFO)
@@ -40,6 +45,7 @@ class ScannerTest(unittest.TestCase):
         os.chdir(self.basedir)
         self._td = mkdtemp()
         self.testdir = self._td.name
+        fdroidserver.scanner.ScannerTool.refresh_allowed = False
 
     def tearDown(self):
         os.chdir(self.basedir)
@@ -712,6 +718,7 @@ class Test_ScannerTool(unittest.TestCase):
         os.chdir(self.basedir)
         self._td = mkdtemp()
         self.testdir = self._td.name
+        fdroidserver.scanner.ScannerTool.refresh_allowed = True
 
     def tearDown(self):
         fdroidserver.common.options = None