diff --git a/src/pystow/impl.py b/src/pystow/impl.py
index bab9445..3f2c612 100644
--- a/src/pystow/impl.py
+++ b/src/pystow/impl.py
@@ -27,6 +27,7 @@
     Optional,
     Sequence,
     Union,
+    cast,
     overload,
 )
 
@@ -875,7 +876,6 @@ def ensure_csv(
         :param download_kwargs: Keyword arguments to pass through to :func:`pystow.utils.download`.
         :param read_csv_kwargs: Keyword arguments to pass through to :func:`pandas.read_csv`.
         :return: A pandas DataFrame
-        :rtype: pandas.DataFrame
         """
         import pandas as pd
 
@@ -1438,7 +1438,6 @@ def ensure_zip_df(
         :param download_kwargs: Keyword arguments to pass through to :func:`pystow.utils.download`.
         :param read_csv_kwargs: Keyword arguments to pass through to :func:`pandas.read_csv`.
         :return: A pandas DataFrame
-        :rtype: pandas.DataFrame
         """
         path = self.ensure(
             *subkeys, url=url, name=name, force=force, download_kwargs=download_kwargs
@@ -1478,7 +1477,6 @@ def ensure_zip_np(
             Additional keyword arguments that are passed through to :func:`read_zip_np`
             and transitively to :func:`numpy.load`.
         :returns: An array-like object
-        :rtype: numpy.typing.ArrayLike
         """
         path = self.ensure(
             *subkeys, url=url, name=name, force=force, download_kwargs=download_kwargs
@@ -1514,7 +1512,6 @@ def ensure_rdf(
             Keyword arguments to pass through to :func:`pystow.utils.read_rdf` and transitively to
             :func:`rdflib.Graph.parse`.
         :return: An RDF graph
-        :rtype: rdflib.Graph
         """
         path = self.ensure(
             *subkeys, url=url, name=name, force=force, download_kwargs=download_kwargs
@@ -1525,7 +1522,7 @@ def ensure_rdf(
         cache_path = path.with_suffix(path.suffix + ".pickle.gz")
         if cache_path.exists() and not force:
             with gzip.open(cache_path, "rb") as file:
-                return pickle.load(file)
+                return cast(rdflib.Graph, pickle.load(file))
 
         rv = read_rdf(path=path, **(parse_kwargs or {}))
         with gzip.open(cache_path, "wb") as file:
diff --git a/src/pystow/utils.py b/src/pystow/utils.py
index c0e7c2d..9e16175 100644
--- a/src/pystow/utils.py
+++ b/src/pystow/utils.py
@@ -31,6 +31,7 @@
     NamedTuple,
     Optional,
     Union,
+    cast,
 )
 from urllib.parse import urlparse
 from urllib.request import urlretrieve
@@ -736,7 +737,7 @@ def read_zip_np(path: Union[str, Path], inner_path: str, **kwargs: Any) -> "nump
 
     with zipfile.ZipFile(file=path) as zip_file:
         with zip_file.open(inner_path) as file:
-            return np.load(file, **kwargs)
+            return cast(np.typing.ArrayLike, np.load(file, **kwargs))
 
 
 def read_zipfile_rdf(path: Union[str, Path], inner_path: str, **kwargs: Any) -> "rdflib.Graph":
@@ -752,7 +753,7 @@ def read_zipfile_rdf(path: Union[str, Path], inner_path: str, **kwargs: Any) ->
     graph = rdflib.Graph()
     with zipfile.ZipFile(file=path) as zip_file:
         with zip_file.open(inner_path) as file:
-            graph.load(file, **kwargs)
+            graph.parse(file, **kwargs)
     return graph
 
 
@@ -809,7 +810,6 @@ def read_tarfile_xml(
     :param inner_path: The path inside the tar archive to the xml file
     :param kwargs: Additional kwargs to pass to :func:`lxml.etree.parse`
     :return: An XML element tree
-    :rtype: lxml.etree.ElementTree
     """
     from lxml import etree
 
@@ -833,7 +833,7 @@ def read_rdf(path: Union[str, Path], **kwargs: Any) -> "rdflib.Graph":
     with (
         gzip.open(path, "rb") if isinstance(path, Path) and path.suffix == ".gz" else open(path)
     ) as file:
-        graph.parse(file, **kwargs)
+        graph.parse(file, **kwargs)  # type:ignore
     return graph
 
 
diff --git a/tox.ini b/tox.ini
index 0ff69bd..dbb7610 100644
--- a/tox.ini
+++ b/tox.ini
@@ -104,7 +104,10 @@ description = Run linters.
 deps =
     mypy
     types-requests
-skip_install = true
+extras =
+    pandas
+    rdf
+    xml
 commands =
     mypy --install-types --non-interactive --ignore-missing-imports --strict src/pystow/
 description = Run the mypy tool to check static typing on the project.