diff --git a/nbgrader/preprocessors/execute.py b/nbgrader/preprocessors/execute.py
index 6f84ee8b1..84bc21e77 100644
--- a/nbgrader/preprocessors/execute.py
+++ b/nbgrader/preprocessors/execute.py
@@ -5,6 +5,7 @@
 from . import NbGraderPreprocessor
 from nbconvert.exporters.exporter import ResourcesDict
 from nbformat.notebooknode import NotebookNode
+from jupyter_client.manager import AsyncKernelManager
 from typing import Any, Optional, Tuple
 
 
@@ -63,6 +64,11 @@ class Execute(NbGraderPreprocessor, ExecutePreprocessor):
         """)
     ).tag(config=True)
 
+    def __init__(self, *args, **kwargs):
+        # nbconvert < 7.3.1 used the sync version of this, which doesn't work for us.
+        kwargs.setdefault('kernel_manager_class', AsyncKernelManager)
+        super().__init__(*args, **kwargs)
+
     def on_cell_executed(self, **kwargs):
         cell = kwargs['cell']
         reply = kwargs['execute_reply']
diff --git a/pyproject.toml b/pyproject.toml
index 41de1a272..56a14c79b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -36,7 +36,7 @@ dependencies = [
     "ipywidgets>=7.6",
     "Jinja2>=3",
     "jsonschema>=3",
-    "jupyter_client<8",
+    "jupyter_client<9",
     "jupyter_server>=1.12,<2",
     "jupyterlab<4",
     "jupyterlab_server",