diff --git a/dev-requirements.txt b/dev-requirements.txt
index 767fe73..269a7e3 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -1,13 +1,13 @@
 # Require a newer fabric than our public API does, since it includes the now
 # public test helpers. Bleh.
-fabric>=2.1.3,<3
+fabric>=3.2,<4
 Sphinx>=1.4,<1.7
 releases>=1.6,<2.0
 alabaster==0.7.12
 wheel==0.24
-twine==1.11.0
-invocations>=1.3.0,<2.0
-pytest-relaxed==1.1.4
+twine==5.1.1
+invocations>=3.0,<4.0
+pytest-relaxed==2.0.2
 coverage==4.4.2
 pytest-cov==2.4.0
 mock==1.0.1
diff --git a/patchwork/files.py b/patchwork/files.py
index 1e68512..eab10b8 100644
--- a/patchwork/files.py
+++ b/patchwork/files.py
@@ -4,8 +4,6 @@
 
 import re
 
-from invoke.vendor import six
-
 from .util import set_runner
 
 
@@ -116,7 +114,7 @@ def append(c, runner, filename, text, partial=False, escape=True):
         Whether to perform regex-oriented escaping on ``text``.
     """
     # Normalize non-list input to be a list
-    if isinstance(text, six.string_types):
+    if isinstance(text, str):
         text = [text]
     for line in text:
         regex = "^" + _escape_for_regex(line) + ("" if partial else "$")
diff --git a/patchwork/transfers.py b/patchwork/transfers.py
index e7292da..df0540a 100644
--- a/patchwork/transfers.py
+++ b/patchwork/transfers.py
@@ -2,8 +2,6 @@
 File transfer functionality above and beyond basic ``put``/``get``.
 """
 
-from invoke.vendor import six
-
 
 def rsync(
     c,
@@ -79,7 +77,7 @@ def rsync(
         (rsync's ``--rsh`` flag.)
     """
     # Turn single-string exclude into a one-item list for consistency
-    if isinstance(exclude, six.string_types):
+    if isinstance(exclude, str):
         exclude = [exclude]
     # Create --exclude options from exclude list
     exclude_opts = ' --exclude "{}"' * len(exclude)
@@ -97,7 +95,7 @@ def rsync(
     # always-a-list, always-up-to-date-from-all-sources attribute to save us
     # from having to do this sort of thing. (may want to wait for Paramiko auth
     # overhaul tho!)
-    if isinstance(keys, six.string_types):
+    if isinstance(keys, str):
         keys = [keys]
     if keys:
         key_string = "-i " + " -i ".join(keys)
diff --git a/patchwork/util.py b/patchwork/util.py
index 705a475..c383a85 100644
--- a/patchwork/util.py
+++ b/patchwork/util.py
@@ -5,7 +5,7 @@
 import textwrap
 
 from functools import wraps
-from inspect import getargspec, formatargspec
+from inspect import signature, Parameter
 
 
 # TODO: calling all functions as eg directory(c, '/foo/bar/') (with initial c)
@@ -126,18 +126,21 @@ def munge_docstring(f, inner):
     # Terrible, awful hacks to ensure Sphinx autodoc sees the intended
     # (modified) signature; leverages the fact that autodoc_docstring_signature
     # is True by default.
-    args, varargs, keywords, defaults = getargspec(f)
+    sig = signature(f)
+    params = sig.parameters
     # Nix positional version of runner arg, which is always 2nd
-    del args[1]
-    # Add new args to end in desired order
-    args.extend(["sudo", "runner_method", "runner"])
-    # Add default values (remembering that this tuple matches the _end_ of the
-    # signature...)
-    defaults = tuple(list(defaults or []) + [False, "run", None])
-    # Get signature first line for Sphinx autodoc_docstring_signature
-    sigtext = "{}{}".format(
-        f.__name__, formatargspec(args, varargs, keywords, defaults)
+    params = [p for i, p in enumerate(params.values()) if i != 1]
+    # Add new args to end in desired order with desired default values
+    params.extend(
+        [
+            Parameter("sudo", Parameter.POSITIONAL_OR_KEYWORD, default=False),
+            Parameter("runner_method", Parameter.POSITIONAL_OR_KEYWORD, default="run"),
+            Parameter("runner", Parameter.POSITIONAL_OR_KEYWORD, default=None),
+        ]
     )
+    sig = sig.replace(parameters=params)
+    # Get signature first line for Sphinx autodoc_docstring_signature
+    sigtext = "{}{}".format(f.__name__, str(sig))
     docstring = textwrap.dedent(inner.__doc__ or "").strip()
     # Construct :param: list
     params = """:param bool sudo:
diff --git a/setup.py b/setup.py
index 0e92cb5..c9f877b 100644
--- a/setup.py
+++ b/setup.py
@@ -19,7 +19,7 @@
     author="Jeff Forcier",
     author_email="jeff@bitprophet.org",
     url="https://fabric-patchwork.readthedocs.io",
-    install_requires=["fabric>=2.0,<3.0"],
+    install_requires=["fabric>=3.0,<4.0"],
     packages=find_packages(),
     classifiers=[
         "Development Status :: 5 - Production/Stable",