diff --git a/sphinx/environment/adapters/toctree.py b/sphinx/environment/adapters/toctree.py
index 182eb956f..a765e8fe9 100644
--- a/sphinx/environment/adapters/toctree.py
+++ b/sphinx/environment/adapters/toctree.py
@@ -322,6 +322,8 @@ class TocTree:
             kwargs['includehidden'] = True
         if 'maxdepth' not in kwargs:
             kwargs['maxdepth'] = 0
+        else:
+            kwargs['maxdepth'] = int(kwargs['maxdepth'])
         kwargs['collapse'] = collapse
         for toctreenode in doctree.traverse(addnodes.toctree):
             toctree = self.resolve(docname, builder, toctreenode, prune=True, **kwargs)