Add const modifier to handle::cast.
diff --git a/docs/reference.rst b/docs/reference.rst
index 16d2a8d..bf7a8e2 100644
--- a/docs/reference.rst
+++ b/docs/reference.rst
@@ -118,7 +118,7 @@
Return a string representation of the object. This is analogous to
the ``str()`` function in Python.
-.. function:: template <typename T> T handle::cast()
+.. function:: template <typename T> T handle::cast() const
Attempt to cast the Python object into the given C++ type. A
:class:`cast_error` will be throw upon failure.