diff --git a/test_runner/fixtures/pageserver/many_tenants.py b/test_runner/fixtures/pageserver/many_tenants.py
index 3e0ffabf74..1a87633042 100644
--- a/test_runner/fixtures/pageserver/many_tenants.py
+++ b/test_runner/fixtures/pageserver/many_tenants.py
@@ -65,7 +65,7 @@ def single_timeline(
             override_storage_controller_generation=True,
         )
 
-    with concurrent.futures.ThreadPoolExecutor(max_workers=22) as executor:
+    with concurrent.futures.ThreadPoolExecutor(max_workers=1) as executor:
         executor.map(attach, tenants)
 
     # Benchmarks will start the pageserver explicitly themselves