diff --git a/src/jupyter_contrib_core/notebook_compat/_compat/nbextensions.py b/src/jupyter_contrib_core/notebook_compat/_compat/nbextensions.py
index e76bdab..6188ea7 100644
--- a/src/jupyter_contrib_core/notebook_compat/_compat/nbextensions.py
+++ b/src/jupyter_contrib_core/notebook_compat/_compat/nbextensions.py
@@ -32,9 +32,15 @@
     ENV_CONFIG_PATH, ENV_JUPYTER_PATH, SYSTEM_CONFIG_PATH, SYSTEM_JUPYTER_PATH,
     jupyter_config_dir, jupyter_data_dir,
 )
-from notebook.nbextensions import (
+try:
+    from notebook.nbextensions import (
     ArgumentConflict, __version__, _safe_is_tarfile,
 )
+except ImportError:
+    from nbclassic.nbextensions import (
+        ArgumentConflict, __version__, _safe_is_tarfile,
+    )
+
 from tornado.log import LogFormatter
 from traitlets import Bool
 from traitlets.config.manager import BaseJSONConfigManager
diff --git a/src/jupyter_contrib_core/notebook_compat/_compat/serverextensions.py b/src/jupyter_contrib_core/notebook_compat/_compat/serverextensions.py
index 32232f4..f3b3d28 100644
--- a/src/jupyter_contrib_core/notebook_compat/_compat/serverextensions.py
+++ b/src/jupyter_contrib_core/notebook_compat/_compat/serverextensions.py
@@ -70,8 +70,8 @@ def toggle_serverextension_python(import_name, enabled=None, parent=None,
     cm = BaseJSONConfigManager(parent=parent, config_dir=config_dir)
     cfg = cm.get("jupyter_notebook_config")
     server_extensions = (
-        cfg.setdefault("NotebookApp", {})
-        .setdefault("server_extensions", [])
+        cfg.setdefault("ServerApp", {})
+        .setdefault("jpserver_extensions", [])
     )
 
     old_enabled = import_name in server_extensions