diff --git a/install.py b/install.py
index 070b3f7..08352dd 100755
--- a/install.py
+++ b/install.py
@@ -38,43 +38,48 @@ class Installer:
     def define_os(self) -> str:
         """Define what OS we are using."""
 
-        os_release = Path("/etc/os-release")
-
         oses = ("arch", "debian", "manjaro", "ubuntu")
+        os_release = Path("/etc/os-release")
+        operating_system = None
+        for operating_system in oses:
+            if operating_system in os_release.read_text().lower():
+                ui.info_3("Found", operating_system, "based distribution")
+                break
 
+        if operating_system is None:
+            ui.warning("Operating system wasn't found")
+            operating_system = input("What is it ? ")
+
+        if operating_system in ("arch", "debian"):
+            self._update_system(operating_system)
+            return operating_system
+
+        ui.fatal("I only support Arch and Debian based distros.")
+        return "Unsupported OS"
+
+    def _update_system(self, operating_system: str) -> None:
         # defaults for subprocess.run()
         this_stdout: Optional[int] = subprocess.DEVNULL if self.hide_commands else None
         this_stderr: Optional[int] = subprocess.DEVNULL if self.hide_commands else None
 
-        for operating_system in oses:
-            if operating_system in os_release.read_text().lower():
-                ui.info_3("Found", operating_system, "based distribution")
+        if operating_system in ("arch", "manjaro"):
+            command = "sudo pacman -Syu"
+            operating_system = "arch"
 
-                if operating_system in ("arch", "manjaro"):
-                    command = "sudo pacman -Syu"
-                    operating_system = "arch"
+        elif operating_system in ("debian", "ubuntu"):
+            command = "sudo apt update"
+            operating_system = "debian"
 
-                if operating_system in ("debian", "ubuntu"):
-                    command = "sudo apt update"
-                    operating_system = "debian"
+        else:
+            raise AssertionError("The operating system should have been defined")
 
-                subprocess.run(
-                    command,
-                    check=True,
-                    shell=True,
-                    stdout=this_stdout,
-                    stderr=this_stderr,
-                )
-                return operating_system
-
-        ui.warning("Operating system wasn't found")
-        operating_system = input("What is it ? ")
-        if operating_system in ("arch", "debian"):
-            return operating_system
-
-        ui.fatal("I only support Arch and Debian based distros.")
-
-        return "Unsupported OS"
+        subprocess.run(
+            command,
+            check=True,
+            shell=True,
+            stdout=this_stdout,
+            stderr=this_stderr,
+        )
 
     def evaluate_condition(self, condition: str) -> bool:
         """Run a bash command. On success return True, else return False."""