diff --git a/dotfiles/vim/vimrc b/dotfiles/vim/vimrc
index b728fe8..34e996c 100644
--- a/dotfiles/vim/vimrc
+++ b/dotfiles/vim/vimrc
@@ -89,8 +89,7 @@ filetype plugin indent on    " required
 
 " PLUGIN OPTIONS {{{
 
-" uncomment to set strict mypy checking
-"let g:ale_python_mypy_options = '--strict --strict-optional'
+let g:ale_python_mypy_options = '--strict --strict-optional'
 
 let g:ycm_extra_conf_globlist = ['!~/*'] " is overwritten in autogroups for c
 let g:ycm_autoclose_preview_window_after_insertion = 1
diff --git a/install.py b/install.py
index c0cdbdf..7456d42 100755
--- a/install.py
+++ b/install.py
@@ -7,19 +7,20 @@ Shamelessly copied from https://github.com/dmerejkowsky/dotfiles.
 
 import argparse
 import subprocess
-from typing import Dict, List, Optional, Tuple
+from typing import List, Optional
 from urllib.request import urlretrieve
 
 import cli_ui as ui  # type: ignore
 from path import Path  # type: ignore
-import ruamel.yaml
+from ruamel.yaml import YAML
 
 
 class Installer:
     """Regroups all the installation methods listed in the yaml conf file."""
 
     def __init__(self, force: bool = False, update: bool = False):
-        self.conf = ruamel.yaml.safe_load(Path("configs.yml").text())
+        yaml = YAML(typ='safe')
+        self.conf = yaml.load(Path("configs.yml").text())
         self.base_dir = Path.getcwd()
         self.home = Path("~").expanduser()
         self.operating_system = define_os()
@@ -105,16 +106,22 @@ class Installer:
         if executable:
             p_dest.chmod(0o755)
 
-    def do_install(self, *packages, **os_specific_packages) -> None:
+    def do_install(
+            self, *packages: str, **os_specific_packages: List[str]
+    ) -> None:
         """Install packages with OS-specific package manager.
 
         Packages can either be in a tuple for non OS-specific packages, or in a
         dict for OS-specific packages.
         """
 
-        if not packages:  # we got the dict, make a list out of it
+        if not packages:
             try:
-                packages = os_specific_packages[self.operating_system] + os_specific_packages["both"]
+                packages = tuple(
+                    os_specific_packages[self.operating_system]
+                    + os_specific_packages["both"]
+                )
+
             except KeyError:
                 ui.fatal("Operating System not understood.")
                 return
@@ -281,7 +288,9 @@ def define_os() -> str:
     if operating_system in ("arch", "debian"):
         return operating_system + " based"
 
-    return ui.fatal("I only support Arch and Debian based distros.")
+    ui.fatal("I only support Arch and Debian based distros.")
+
+    return "Unsupported OS"
 
 
 def main() -> None: