diff --git a/mypy.ini b/mypy.ini
index 9c05db2..5bb8894 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -2,7 +2,8 @@
 python_version = 3.8
 color_output = True
 error_summary = True
-; disallow_untyped_calls = True
+check_untyped_defs = true
+disallow_untyped_calls = True
 ; disallow_untyped_defs = True
 ; disallow_any_generics = True
 ; disallow_any_unimported = True
diff --git a/src/vagrant/__init__.py b/src/vagrant/__init__.py
index 6b8282e..299a156 100644
--- a/src/vagrant/__init__.py
+++ b/src/vagrant/__init__.py
@@ -19,6 +19,8 @@
 import subprocess
 import sys
 import logging
+import typing
+from typing import Dict, Iterator, List, Optional, Union
 
 # local
 from . import compat
@@ -42,7 +44,7 @@
 )
 
 
-def which(program):  # noqa C901
+def which(program) -> Optional[str]:  # noqa C901
     """
     Emulate unix 'which' command.  If program is a path to an executable file
     (i.e. it contains any directory components, like './myscript'), return
@@ -62,7 +64,7 @@ def which(program):  # noqa C901
     https://hg.python.org/cpython/file/default/Lib/shutil.py
     """
 
-    def is_exe(fpath):
+    def is_exe(fpath) -> bool:
         return os.path.isfile(fpath) and os.access(fpath, os.X_OK)
 
     # Shortcut: If program contains any dir components, do not search the path
@@ -128,7 +130,7 @@ def is_exe(fpath):
 
 
 # The full path to the vagrant executable, e.g. '/usr/bin/vagrant'
-def get_vagrant_executable():
+def get_vagrant_executable() -> Optional[str]:
     return which("vagrant")
 
 
@@ -174,7 +176,7 @@ def none_cm():
     yield None
 
 
-def make_file_cm(filename, mode="a"):
+def make_file_cm(filename, mode="a") -> typing.Callable[[], typing.ContextManager]:
     """
     Open a file for appending and yield the open filehandle.  Close the
     filehandle after yielding it.  This is useful for creating a context
@@ -230,7 +232,7 @@ def __init__(
         env=None,
         out_cm=None,
         err_cm=None,
-    ):
+    ) -> None:
         """
         root: a directory containing a file named Vagrantfile.  Defaults to
           os.getcwd(). This is the directory and Vagrantfile that the Vagrant
@@ -258,8 +260,8 @@ def __init__(
           will be sent to devnull.
         """
         self.root = os.path.abspath(root) if root is not None else os.getcwd()
-        self._cached_conf = {}
-        self._vagrant_exe = None  # cache vagrant executable path
+        self._cached_conf: Dict[str, Optional[Dict[str, str]]] = {}
+        self._vagrant_exe: Optional[str] = None  # cache vagrant executable path
         self.env = env
         if out_cm is not None:
             self.out_cm = out_cm
@@ -279,7 +281,7 @@ def __init__(
         else:
             self.err_cm = none_cm
 
-    def version(self):
+    def version(self) -> str:
         """
         Return the installed vagrant version, as a string, e.g. '1.5.0'
         """
@@ -291,7 +293,7 @@ def version(self):
             )
         return m.group("version")
 
-    def init(self, box_name=None, box_url=None):
+    def init(self, box_name=None, box_url=None) -> None:
         """
         From the Vagrant docs:
 
@@ -315,7 +317,7 @@ def up(
         provision=None,
         provision_with=None,
         stream_output=False,
-    ):
+    ) -> Optional[Iterator[str]]:
         """
         Invoke `vagrant up` to start a box or boxes, possibly streaming the
         command output.
@@ -368,7 +370,7 @@ def up(
         self._cached_conf[vm_name] = None  # remove cached configuration
         return generator if stream_output else None
 
-    def provision(self, vm_name=None, provision_with=None):
+    def provision(self, vm_name=None, provision_with=None) -> None:
         """
         Runs the provisioners defined in the Vagrantfile.
         vm_name: optional VM name string.
@@ -381,7 +383,7 @@ def provision(self, vm_name=None, provision_with=None):
 
     def reload(
         self, vm_name=None, provision=None, provision_with=None, stream_output=False
-    ):
+    ) -> Optional[Iterator[str]]:
         """
         Quoting from Vagrant docs:
         > The equivalent of running a halt followed by an up.
@@ -421,21 +423,21 @@ def reload(
         self._cached_conf[vm_name] = None  # remove cached configuration
         return generator if stream_output else None
 
-    def suspend(self, vm_name=None):
+    def suspend(self, vm_name=None) -> None:
         """
         Suspend/save the machine.
         """
         self._call_vagrant_command(["suspend", vm_name])
         self._cached_conf[vm_name] = None  # remove cached configuration
 
-    def resume(self, vm_name=None):
+    def resume(self, vm_name=None) -> None:
         """
         Resume suspended machine.
         """
         self._call_vagrant_command(["resume", vm_name])
         self._cached_conf[vm_name] = None  # remove cached configuration
 
-    def halt(self, vm_name=None, force=False):
+    def halt(self, vm_name=None, force=False) -> None:
         """
         Halt the Vagrant box.
 
@@ -445,14 +447,14 @@ def halt(self, vm_name=None, force=False):
         self._call_vagrant_command(["halt", vm_name, force_opt])
         self._cached_conf[vm_name] = None  # remove cached configuration
 
-    def destroy(self, vm_name=None):
+    def destroy(self, vm_name=None) -> None:
         """
         Terminate the running Vagrant box.
         """
         self._call_vagrant_command(["destroy", vm_name, "--force"])
         self._cached_conf[vm_name] = None  # remove cached configuration
 
-    def status(self, vm_name=None):
+    def status(self, vm_name=None) -> List[Status]:
         r"""
         Return the results of a `vagrant status` call as a list of one or more
         Status objects.  A Status contains the following attributes:
@@ -546,7 +548,7 @@ def global_status(self, prune=False):
         output = self._run_vagrant_command(cmd)
         return self._parse_global_status(output)
 
-    def _normalize_status(self, status, provider):
+    def _normalize_status(self, status, provider) -> str:
         """
         Normalise VM status to cope with state name being different
         between providers
@@ -562,7 +564,7 @@ def _normalize_status(self, status, provider):
 
         return status
 
-    def _parse_status(self, output):
+    def _parse_status(self, output) -> List[Status]:
         """
         Unit testing is so much easier when Vagrant is removed from the
         equation.
@@ -583,7 +585,7 @@ def _parse_status(self, output):
 
         return statuses
 
-    def _parse_global_status(self, output):
+    def _parse_global_status(self, output: str) -> List[GlobalStatus]:
         """
         Unit testing is so much easier when Vagrant is removed from the
         equation.
@@ -609,7 +611,7 @@ def _parse_global_status(self, output):
                 vm_id = state = provider = home = None
         return statuses
 
-    def conf(self, ssh_config=None, vm_name=None):
+    def conf(self, ssh_config=None, vm_name=None) -> Dict[str, str]:
         """
         Parse ssh_config into a dict containing the keys defined in ssh_config,
         which should include these keys (listed with example values): 'User'
@@ -631,15 +633,15 @@ def conf(self, ssh_config=None, vm_name=None):
         the value returned from ssh_config().  For speed, the configuration
         parsed from ssh_config is cached for subsequent calls.
         """
-        if self._cached_conf.get(vm_name) is None or ssh_config is not None:
+        conf = self._cached_conf.get(vm_name)
+        if conf is None or ssh_config is not None:
             if ssh_config is None:
                 ssh_config = self.ssh_config(vm_name=vm_name)
             conf = self._parse_config(ssh_config)
             self._cached_conf[vm_name] = conf
+        return conf
 
-        return self._cached_conf[vm_name]
-
-    def ssh_config(self, vm_name=None):
+    def ssh_config(self, vm_name=None) -> str:
         """
         Return the output of 'vagrant ssh-config' which appears to be a valid
         Host section suitable for use in an ssh config file.
@@ -662,7 +664,7 @@ def ssh_config(self, vm_name=None):
         # capture ssh configuration from vagrant
         return self._run_vagrant_command(["ssh-config", vm_name])
 
-    def user(self, vm_name=None):
+    def user(self, vm_name=None) -> Optional[str]:
         """
         Return the ssh user of the vagrant box, e.g. 'vagrant'
         or None if there is no user in the ssh_config.
@@ -672,7 +674,7 @@ def user(self, vm_name=None):
         """
         return self.conf(vm_name=vm_name).get("User")
 
-    def hostname(self, vm_name=None):
+    def hostname(self, vm_name=None) -> Optional[str]:
         """
         Return the vagrant box hostname, e.g. '127.0.0.1'
         or None if there is no hostname in the ssh_config.
@@ -682,7 +684,7 @@ def hostname(self, vm_name=None):
         """
         return self.conf(vm_name=vm_name).get("HostName")
 
-    def port(self, vm_name=None):
+    def port(self, vm_name=None) -> Optional[str]:
         """
         Return the vagrant box ssh port, e.g. '2222'
         or None if there is no port in the ssh_config.
@@ -692,7 +694,7 @@ def port(self, vm_name=None):
         """
         return self.conf(vm_name=vm_name).get("Port")
 
-    def keyfile(self, vm_name=None):
+    def keyfile(self, vm_name=None) -> Optional[str]:
         """
         Return the path to the private key used to log in to the vagrant box
         or None if there is no keyfile (IdentityFile) in the ssh_config.
@@ -705,7 +707,7 @@ def keyfile(self, vm_name=None):
         """
         return self.conf(vm_name=vm_name).get("IdentityFile")
 
-    def user_hostname(self, vm_name=None):
+    def user_hostname(self, vm_name=None) -> str:
         """
         Return a string combining user and hostname, e.g. 'vagrant@127.0.0.1'.
         This string is suitable for use in an ssh command.  If user is None
@@ -716,10 +718,13 @@ def user_hostname(self, vm_name=None):
         has been destroyed.
         """
         user = self.user(vm_name=vm_name)
+        hostname = self.hostname(vm_name=vm_name)
+        if hostname is None:
+            raise ValueError("Missing hostname for vm_name={vm_name!r}")
         user_prefix = user + "@" if user else ""
-        return user_prefix + self.hostname(vm_name=vm_name)
+        return user_prefix + hostname
 
-    def user_hostname_port(self, vm_name=None):
+    def user_hostname_port(self, vm_name=None) -> str:
         """
         Return a string combining user, hostname and port, e.g.
         'vagrant@127.0.0.1:2222'.  This string is suitable for use with Fabric,
@@ -733,11 +738,14 @@ def user_hostname_port(self, vm_name=None):
         """
         user = self.user(vm_name=vm_name)
         port = self.port(vm_name=vm_name)
+        hostname = self.hostname(vm_name=vm_name)
+        if hostname is None:
+            raise ValueError("Missing hostname for vm_name={vm_name!r}")
         user_prefix = user + "@" if user else ""
         port_suffix = ":" + port if port else ""
-        return user_prefix + self.hostname(vm_name=vm_name) + port_suffix
+        return user_prefix + hostname + port_suffix
 
-    def box_add(self, name, url, provider=None, force=False):
+    def box_add(self, name, url, provider=None, force=False) -> None:
         """
         Adds a box with given name, from given url.
 
@@ -750,7 +758,7 @@ def box_add(self, name, url, provider=None, force=False):
 
         self._call_vagrant_command(cmd)
 
-    def box_list(self):
+    def box_list(self) -> List[Box]:
         """
         Run `vagrant box list --machine-readable` and return a list of Box
         objects containing the results.  A Box object has the following
@@ -847,7 +855,7 @@ def snapshot_delete(self, name):
         """
         self._call_vagrant_command(["snapshot", "delete", name])
 
-    def ssh(self, vm_name=None, command=None, extra_ssh_args=None):
+    def ssh(self, vm_name=None, command=None, extra_ssh_args=None) -> str:
         """
         Execute a command via ssh on the vm specified.
         command: The command to execute via ssh.
@@ -860,7 +868,7 @@ def ssh(self, vm_name=None, command=None, extra_ssh_args=None):
 
         return self._run_vagrant_command(cmd)
 
-    def _parse_box_list(self, output):
+    def _parse_box_list(self, output) -> List[Box]:
         """
         Remove Vagrant usage for unit testing
         """
@@ -891,14 +899,14 @@ def _parse_box_list(self, output):
 
         return boxes
 
-    def box_update(self, name, provider):
+    def box_update(self, name, provider) -> None:
         """
         Updates the box matching name and provider. It is an error if no box
         matches name and provider.
         """
         self._call_vagrant_command(["box", "update", name, provider])
 
-    def box_remove(self, name, provider):
+    def box_remove(self, name, provider) -> None:
         """
         Removes the box matching name and provider. It is an error if no box
         matches name and provider.
@@ -941,7 +949,7 @@ def plugin_list(self):
         output = self._run_vagrant_command(["plugin", "list", "--machine-readable"])
         return self._parse_plugin_list(output)
 
-    def validate(self, directory):
+    def validate(self, directory) -> subprocess.CompletedProcess:
         """
         This command validates present Vagrantfile.
         """
@@ -955,7 +963,7 @@ def validate(self, directory):
 
         return validate
 
-    def _parse_plugin_list(self, output):
+    def _parse_plugin_list(self, output) -> List[Plugin]:
         """
         Remove Vagrant from the equation for unit testing.
         """
@@ -992,7 +1000,7 @@ def _parse_plugin_list(self, output):
 
         return plugins
 
-    def _parse_machine_readable_output(self, output):
+    def _parse_machine_readable_output(self, output: str) -> List[List[str]]:
         """Parse machine readable output from vagrant commands.
 
         param output: a string containing the output of a vagrant command with the `--machine-readable` option.
@@ -1023,7 +1031,7 @@ def _parse_machine_readable_output(self, output):
         parsed_lines = list(filter(lambda x: x[2] not in unneeded_kind, parsed_lines))
         return parsed_lines
 
-    def _parse_config(self, ssh_config):
+    def _parse_config(self, ssh_config: str) -> Dict[str, str]:
         r"""
         This lame parser does not parse the full grammar of an ssh config
         file.  It makes assumptions that are (hopefully) correct for the output
@@ -1058,7 +1066,7 @@ def _parse_config(self, ssh_config):
             conf[key] = value.strip('"')
         return conf
 
-    def _make_vagrant_command(self, args):
+    def _make_vagrant_command(self, args: List[Union[str, None]]) -> List[str]:
         if self._vagrant_exe is None:
             self._vagrant_exe = get_vagrant_executable()
 
@@ -1070,7 +1078,7 @@ def _make_vagrant_command(self, args):
         # when it is not specified.
         return [self._vagrant_exe] + [arg for arg in args if arg is not None]
 
-    def _call_vagrant_command(self, args):
+    def _call_vagrant_command(self, args) -> None:
         """
         Run a vagrant command.  Return None.
         args: A sequence of arguments to a vagrant command line.
@@ -1083,7 +1091,7 @@ def _call_vagrant_command(self, args):
                 command, cwd=self.root, stdout=out_fh, stderr=err_fh, env=self.env
             )
 
-    def _run_vagrant_command(self, args):
+    def _run_vagrant_command(self, args) -> str:
         """
         Run a vagrant command and return its stdout.
         args: A sequence of arguments to a vagrant command line.
@@ -1099,7 +1107,7 @@ def _run_vagrant_command(self, args):
                 )
             )
 
-    def _stream_vagrant_command(self, args):
+    def _stream_vagrant_command(self, args) -> Iterator[str]:
         """
         Execute a vagrant command, returning a generator of the output lines.
         Caller should consume the entire generator to avoid the hanging the
@@ -1123,8 +1131,9 @@ def _stream_vagrant_command(self, args):
             # Iterate over output lines.
             # See http://stackoverflow.com/questions/2715847/python-read-streaming-input-from-subprocess-communicate#17698359
             with subprocess.Popen(**sp_args) as p:
-                with p.stdout:
-                    for line in iter(p.stdout.readline, b""):
+                stdout = typing.cast(typing.IO, p.stdout)
+                with stdout:
+                    for line in iter(stdout.readline, b""):
                         yield compat.decode(line)  # if PY3 decode bytestrings
                 p.wait()
                 # Raise CalledProcessError for consistency with _call_vagrant_command
@@ -1137,22 +1146,22 @@ class SandboxVagrant(Vagrant):
     Support for sandbox mode using the Sahara gem (https://github.com/jedi4ever/sahara).
     """
 
-    def _run_sandbox_command(self, args):
+    def _run_sandbox_command(self, args) -> str:
         return self._run_vagrant_command(["sandbox"] + list(args))
 
-    def sandbox_commit(self, vm_name=None):
+    def sandbox_commit(self, vm_name=None) -> None:
         """
         Permanently writes all the changes made to the VM.
         """
         self._run_sandbox_command(["commit", vm_name])
 
-    def sandbox_off(self, vm_name=None):
+    def sandbox_off(self, vm_name=None) -> None:
         """
         Disables the sandbox mode.
         """
         self._run_sandbox_command(["off", vm_name])
 
-    def sandbox_on(self, vm_name=None):
+    def sandbox_on(self, vm_name=None) -> None:
         """
         Enables the sandbox mode.
 
@@ -1161,13 +1170,13 @@ def sandbox_on(self, vm_name=None):
         """
         self._run_sandbox_command(["on", vm_name])
 
-    def sandbox_rollback(self, vm_name=None):
+    def sandbox_rollback(self, vm_name=None) -> None:
         """
         Reverts all the changes made to the VM since the last commit.
         """
         self._run_sandbox_command(["rollback", vm_name])
 
-    def sandbox_status(self, vm_name=None):
+    def sandbox_status(self, vm_name=None) -> str:
         """
         Returns the status of the sandbox mode.
 
@@ -1180,7 +1189,7 @@ def sandbox_status(self, vm_name=None):
         vagrant_sandbox_output = self._run_sandbox_command(["status", vm_name])
         return self._parse_vagrant_sandbox_status(vagrant_sandbox_output)
 
-    def _parse_vagrant_sandbox_status(self, vagrant_output):
+    def _parse_vagrant_sandbox_status(self, vagrant_output) -> str:
         """
         Returns the status of the sandbox mode given output from
         'vagrant sandbox status'.
diff --git a/src/vagrant/compat.py b/src/vagrant/compat.py
index 22f6f17..f520acf 100644
--- a/src/vagrant/compat.py
+++ b/src/vagrant/compat.py
@@ -13,7 +13,7 @@
 PY2 = sys.version_info[0] == 2
 
 
-def decode(value):
+def decode(value: bytes) -> str:
     """Decode binary data to text if needed (for Python 3).
 
     Use with the functions that return in Python 2 value of `str` type and for Python 3 encoded bytes.
@@ -21,4 +21,4 @@ def decode(value):
     :param value: Encoded bytes for Python 3 and `str` for Python 2.
     :return: Value as a text.
     """
-    return value.decode(locale.getpreferredencoding()) if not PY2 else value
+    return value.decode(locale.getpreferredencoding()) if not PY2 else value  # type: ignore
diff --git a/src/vagrant/test.py b/src/vagrant/test.py
index 2287144..457319d 100644
--- a/src/vagrant/test.py
+++ b/src/vagrant/test.py
@@ -4,7 +4,7 @@
 It also removes some of the boilerplate involved in writing tests that leverage
 vagrant boxes.
 """
-from typing import Dict, List
+from typing import Dict, List, Optional
 from unittest import TestCase
 from vagrant import Vagrant, stderr_cm
 
@@ -22,7 +22,7 @@ class VagrantTestCase(TestCase):
     """
 
     vagrant_boxes: List[str] = []
-    vagrant_root = None
+    vagrant_root: Optional[str] = None
     restart_boxes = False
 
     __initial_box_statuses: Dict[str, str] = {}
@@ -43,7 +43,7 @@ def __init__(self, *args, **kwargs):
                 self.vagrant_boxes = boxes
         super().__init__(*args, **kwargs)
 
-    def assertBoxStatus(self, box, status):
+    def assertBoxStatus(self, box: str, status: str) -> None:
         """Assertion for a box status"""
         box_status = [s.state for s in self.vagrant.status() if s.name == box][0]
         if box_status != status:
@@ -51,19 +51,19 @@ def assertBoxStatus(self, box, status):
                 "{} has status {}, not {}".format(box, box_status, status)
             )
 
-    def assertBoxUp(self, box):
+    def assertBoxUp(self, box: str) -> None:
         """Assertion for a box being up"""
         self.assertBoxStatus(box, Vagrant.RUNNING)
 
-    def assertBoxSuspended(self, box):
+    def assertBoxSuspended(self, box: str) -> None:
         """Assertion for a box being up"""
         self.assertBoxStatus(box, Vagrant.SAVED)
 
-    def assertBoxHalted(self, box):
+    def assertBoxHalted(self, box: str) -> None:
         """Assertion for a box being up"""
         self.assertBoxStatus(box, Vagrant.POWEROFF)
 
-    def assertBoxNotCreated(self, box):
+    def assertBoxNotCreated(self, box: str) -> None:
         """Assertion for a box being up"""
         self.assertBoxStatus(box, Vagrant.NOT_CREATED)
 
@@ -74,18 +74,18 @@ def run(self, result=None):
         self.tearDownOnce()
         return run
 
-    def setUpOnce(self):
+    def setUpOnce(self) -> None:
         """Collect the box states before starting"""
         for box_name in self.vagrant_boxes:
             s = self.vagrant.status(vm_name=box_name)[0]
             self.__initial_box_statuses[box_name] = s.state
 
-    def tearDownOnce(self):
+    def tearDownOnce(self) -> None:
         """Restore all boxes to their initial states after running all tests, unless tearDown handled it already"""
         if not self.restart_boxes:
             self.restore_box_states()
 
-    def restore_box_states(self):
+    def restore_box_states(self) -> None:
         """Restores all boxes to their original states"""
         for box_name in self.vagrant_boxes:
             action = self.__cleanup_actions.get(self.__initial_box_statuses[box_name])
diff --git a/tests/test_vagrant.py b/tests/test_vagrant.py
index d35089d..f35d2b6 100644
--- a/tests/test_vagrant.py
+++ b/tests/test_vagrant.py
@@ -22,7 +22,8 @@
 import sys
 import tempfile
 import time
-from typing import Generator
+import typing
+from typing import Generator, List, Optional
 
 
 import pytest
@@ -46,7 +47,7 @@ def get_provider() -> str:
 
 
 # location of Vagrant executable
-VAGRANT_EXE = vagrant.get_vagrant_executable()
+VAGRANT_EXE = typing.cast(str, vagrant.get_vagrant_executable())
 
 # location of a test file on the created box by provisioning in vm_Vagrantfile
 TEST_FILE_PATH = "/home/vagrant/python_vagrant_test_file"
@@ -106,7 +107,7 @@ def fixture_test_dir() -> Generator[str, None, None]:
         shutil.rmtree(my_dir)
 
 
-def list_box_names():
+def list_box_names() -> List[str]:
     """
     Return a list of the currently installed vagrant box names.  This is
     implemented outside of `vagrant.Vagrant`, so that it will still work
@@ -714,7 +715,7 @@ def test_streaming_output(vm_dir):
         v.up(vm_name="incorrect-name")
 
     streaming_up = False
-    for line in v.up(stream_output=True):
+    for line in v.up(stream_output=True):  # type: ignore
         print("output line:", line)
         if test_string in line:
             streaming_up = True
@@ -722,7 +723,7 @@ def test_streaming_output(vm_dir):
     assert streaming_up
 
     streaming_reload = False
-    for line in v.reload(stream_output=True):
+    for line in v.reload(stream_output=True):  # type: ignore
         print("output line:", line)
         if test_string in line:
             streaming_reload = True
@@ -759,7 +760,7 @@ def test_vagrant_version():
     assert version_result is True
 
 
-def _execute_command_in_vm(v, command):
+def _execute_command_in_vm(v, command) -> str:
     """
     Run command via ssh on the test vagrant box.  Returns a tuple of the
     return code and output of the command.
@@ -769,7 +770,7 @@ def _execute_command_in_vm(v, command):
     return compat.decode(subprocess.check_output(ssh_command, cwd=v.root))
 
 
-def _write_test_file(v, file_contents):
+def _write_test_file(v, file_contents) -> None:
     """
     Writes given contents to the test file.
     """
@@ -777,7 +778,7 @@ def _write_test_file(v, file_contents):
     _execute_command_in_vm(v, command)
 
 
-def _read_test_file(v):
+def _read_test_file(v) -> Optional[str]:
     """
     Returns the contents of the test file stored in the VM or None if there
     is no file.
@@ -790,6 +791,6 @@ def _read_test_file(v):
         return None
 
 
-def _plugin_installed(v, plugin_name):
+def _plugin_installed(v, plugin_name) -> bool:
     plugins = v.plugin_list()
     return plugin_name in [plugin.name for plugin in plugins]
diff --git a/tests/test_vagrant_test_case.py b/tests/test_vagrant_test_case.py
index 7519db6..43945ee 100644
--- a/tests/test_vagrant_test_case.py
+++ b/tests/test_vagrant_test_case.py
@@ -9,7 +9,7 @@
 from .test_vagrant import TEST_BOX_NAME
 
 
-def get_vagrant_root(test_vagrant_root_path):
+def get_vagrant_root(test_vagrant_root_path) -> str:
     return (
         os.path.dirname(os.path.realpath(__file__))
         + "/vagrantfiles/"