diff --git a/sphinx/environment/adapters/toctree.py b/sphinx/environment/adapters/toctree.py
index 182eb956f..93555d172 100644
--- a/sphinx/environment/adapters/toctree.py
+++ b/sphinx/environment/adapters/toctree.py
@@ -320,8 +320,10 @@ class TocTree:
         toctrees = []  # type: List[Element]
         if 'includehidden' not in kwargs:
             kwargs['includehidden'] = True
-        if 'maxdepth' not in kwargs:
+        if 'maxdepth' not in kwargs or not kwargs['maxdepth']:
             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)