diff --git a/contrib/perf.py b/contrib/perf.py
index 42dd6ec73c28d0aa5d00f485501795926602bc02_Y29udHJpYi9wZXJmLnB5..6a7b0d0f090da78d656c5321a280def8a96a021b_Y29udHJpYi9wZXJmLnB5 100644
--- a/contrib/perf.py
+++ b/contrib/perf.py
@@ -2240,7 +2240,7 @@
 
     @contextlib.contextmanager
     def context():
-        with open(filename, mode='rb') as bundle:
+        with open(filename, mode='rb', buffering=0) as bundle:
             bundle_name = bundle.name
             if opts.get(b'in_memory_bundle'):
                 # you hate memory, don't you?