diff --git a/pipenv/environment.py b/pipenv/environment.py
index 94193b28..f3c2e898 100644
--- a/pipenv/environment.py
+++ b/pipenv/environment.py
@@ -18,6 +18,7 @@ from pipenv.patched.pip._internal.req.req_uninstall import UninstallPathSet
 from pipenv.patched.pip._vendor import pkg_resources
 from pipenv.patched.pip._vendor.packaging.utils import canonicalize_name
 from pipenv.utils.constants import is_type_checking
+from pipenv.utils.funktools import chunked, unnest
 from pipenv.utils.indexes import prepare_pip_source_args
 from pipenv.utils.processes import subprocess_run
 from pipenv.utils.shell import make_posix, normalize_path
@@ -714,8 +715,6 @@ class Environment:
         yield new_node
 
     def reverse_dependencies(self):
-        from vistir.misc import chunked, unnest
-
         rdeps = {}
         for req in self.get_package_requirements():
             for d in self.reverse_dependency(req):
diff --git a/pipenv/utils/funktools.py b/pipenv/utils/funktools.py
new file mode 100644
index 00000000..bcfeae5e
--- /dev/null
+++ b/pipenv/utils/funktools.py
@@ -0,0 +1,69 @@
+"""
+A small collection of useful functional tools for working with iterables.
+"""
+from functools import islice, partial, tee
+
+from typings import Any, Iterable
+
+
+def _is_iterable(elem: Any) -> bool:
+    if getattr(elem, "__iter__", False) or isinstance(elem, Iterable):
+        return True
+    return False
+
+
+def take(n: int, iterable: Iterable) -> Iterable:
+    """Take n elements from the supplied iterable without consuming it.
+
+    :param int n: Number of unique groups
+    :param iter iterable: An iterable to split up
+    """
+    return list(islice(iterable, n))
+
+
+def chunked(n: int, iterable: Iterable) -> Iterable:
+    """Split an iterable into lists of length *n*.
+
+    :param int n: Number of unique groups
+    :param iter iterable: An iterable to split up
+
+    """
+    return iter(partial(take, n, iter(iterable)), [])
+
+
+def unnest(elem: Iterable) -> Any:
+    # type: (Iterable) -> Any
+    """Flatten an arbitrarily nested iterable.
+
+    :param elem: An iterable to flatten
+    :type elem: :class:`~collections.Iterable`
+    >>> nested_iterable = (
+            1234, (3456, 4398345, (234234)), (
+                2396, (
+                    928379, 29384, (
+                        293759, 2347, (
+                            2098, 7987, 27599
+                        )
+                    )
+                )
+            )
+        )
+    >>> list(unnest(nested_iterable))
+    [1234, 3456, 4398345, 234234, 2396, 928379, 29384, 293759,
+     2347, 2098, 7987, 27599]
+    """
+
+    if isinstance(elem, Iterable) and not isinstance(elem, str):
+        elem, target = tee(elem, 2)
+    else:
+        target = elem
+    if not target or not _is_iterable(target):
+        yield target
+    else:
+        for el in target:
+            if isinstance(el, Iterable) and not isinstance(el, str):
+                el, el_copy = tee(el, 2)
+                for sub in unnest(el_copy):
+                    yield sub
+            else:
+                yield el