diff --git a/tests/artifacts/cache/big-file-churn.hg.md5 b/tests/artifacts/cache/big-file-churn.hg.md5
--- a/tests/artifacts/cache/big-file-churn.hg.md5
+++ b/tests/artifacts/cache/big-file-churn.hg.md5
@@ -1,1 +1,1 @@
-403f5c247ad7cf58d3fad247a6b5e731
+cb1e67ae6b17ba66dd455f9782692f4a
diff --git a/tests/artifacts/scripts/generate-churning-bundle.py b/tests/artifacts/scripts/generate-churning-bundle.py
--- a/tests/artifacts/scripts/generate-churning-bundle.py
+++ b/tests/artifacts/scripts/generate-churning-bundle.py
@@ -119,7 +119,7 @@ def run(target):
                 hg('merge', 'min(head())')
             updatefile(FILENAME, idx)
             hg('commit', '--message', 'commit #%d' % idx)
-        hg('bundle', '--all', target)
+        hg('bundle', '--all', target, '--config', 'devel.bundle.delta=p1')
         with open(target, 'rb') as bundle:
             data = bundle.read()
             digest = hashlib.md5(data).hexdigest()