diff --git a/src/calibre/db/tests/base.py b/src/calibre/db/tests/base.py
index b94faf6b28..dd87ab1583 100644
--- a/src/calibre/db/tests/base.py
+++ b/src/calibre/db/tests/base.py
@@ -21,6 +21,11 @@ class BaseTest(unittest.TestCase):
     longMessage = True
     maxDiff = None
 
+    @classmethod
+    def setUpClass(cls):
+        from calibre.utils.config_base import reset_tweaks_to_default
+        reset_tweaks_to_default()
+
     def setUp(self):
         self.library_path = self.mkdtemp()
         self.create_db(self.library_path)
diff --git a/src/calibre/utils/config_base.py b/src/calibre/utils/config_base.py
index a31b7052b1..a9860b60fa 100644
--- a/src/calibre/utils/config_base.py
+++ b/src/calibre/utils/config_base.py
@@ -474,4 +474,11 @@ def write_tweaks(raw):
 
 tweaks = read_tweaks()
 
+def reset_tweaks_to_default():
+    global tweaks
+    default_tweaks = P('default_tweaks.py', data=True,
+            allow_user_override=False)
+    dl, dg = {}, {}
+    exec default_tweaks in dg, dl
+    tweaks = dl