diff --git a/jupyterhub/singleuser/extension.py b/jupyterhub/singleuser/extension.py
index f5e2f197..3859b6a9 100644
--- a/jupyterhub/singleuser/extension.py
+++ b/jupyterhub/singleuser/extension.py
@@ -617,7 +617,9 @@ class JupyterHubSingleUser(ExtensionApp):
         app.web_app.settings[
             "page_config_hook"
         ] = app.identity_provider.page_config_hook
-        app.web_app.settings["log_function"] = log_request
+        # if the user has configured a log function in the tornado settings, do not override it
+        if not 'log_function' in app.config.ServerApp.get('tornado_settings', {}):
+            app.web_app.settings["log_function"] = log_request
         # add jupyterhub version header
         headers = app.web_app.settings.setdefault("headers", {})
         headers["X-JupyterHub-Version"] = __version__
diff --git a/jupyterhub/singleuser/mixins.py b/jupyterhub/singleuser/mixins.py
index 723ff961..8ab43d36 100755
--- a/jupyterhub/singleuser/mixins.py
+++ b/jupyterhub/singleuser/mixins.py
@@ -669,7 +669,8 @@ class SingleUserNotebookAppMixin(Configurable):
         # load the hub-related settings into the tornado settings dict
         self.init_hub_auth()
         s = self.tornado_settings
-        s['log_function'] = log_request
+        # if the user has configured a log function in the tornado settings, do not override it
+        s.setdefault('log_function', log_request)
         s['user'] = self.user
         s['group'] = self.group
         s['hub_prefix'] = self.hub_prefix