diff --git a/tests/conftest.py b/tests/conftest.py
index 32524e0ca..764cc8047 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -11,6 +11,7 @@
 import zmq_anyio
 from anyio import create_memory_object_stream, create_task_group, sleep
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
+from IPython.core.history import HistoryManager
 from jupyter_client.session import Session
 
 from ipykernel.ipkernel import IPythonKernel
@@ -34,6 +35,9 @@ def _garbage_collection(request):
 except ModuleNotFoundError:
     tracemalloc = None
 
+# ensure we don't leak history managers
+HistoryManager._max_inst = 2
+
 pytestmark = pytest.mark.anyio