diff --git a/src/pywinbox/_pywinbox_linux.py b/src/pywinbox/_pywinbox_linux.py
index c97180d..9622a43 100644
--- a/src/pywinbox/_pywinbox_linux.py
+++ b/src/pywinbox/_pywinbox_linux.py
@@ -2,9 +2,15 @@
 from __future__ import annotations
 
 import sys
+if sys.platform != "linux":
+    raise OSError(f"Cannot import {__name__} on {sys.platform}")
+
 import os
 
+from ._main import Box
+
 try:
+    # TypeAlias does not exist in typing for Python3.9
     from typing import TypeAlias
 except Exception:
     from typing import TYPE_CHECKING
@@ -13,12 +19,8 @@
 from typing import Union
 
 from Xlib.xobject.drawable import Window as XWindow
-
-from ._main import Box
 from ewmhlib import EwmhWindow
 
-assert sys.platform == "linux"
-
 
 _HandleTypeIn: TypeAlias = Union[int, XWindow, None]
 _HandleTypeOut: TypeAlias = Union[EwmhWindow, None]
diff --git a/src/pywinbox/_pywinbox_macos.py b/src/pywinbox/_pywinbox_macos.py
index a32c2ba..403267c 100644
--- a/src/pywinbox/_pywinbox_macos.py
+++ b/src/pywinbox/_pywinbox_macos.py
@@ -3,10 +3,16 @@
 # mypy: disable_error_code = no-any-return
 from __future__ import annotations
 
-import subprocess
 import sys
+if sys.platform != "darwin":
+    raise OSError(f"Cannot import {__name__} on {sys.platform}")
+
+import subprocess
+
+from ._main import Box
 
 try:
+    # TypeAlias does not exist in typing for Python3.9
     from typing import TypeAlias
 except Exception:
     from typing import TYPE_CHECKING
@@ -14,11 +20,8 @@
         from typing_extensions import TypeAlias
 from typing import NamedTuple, cast, Union
 
-from ._main import Box
 import AppKit
 
-assert sys.platform == "darwin"
-
 
 class _macOSNSHandle(NamedTuple):
     isNSHandle: bool
diff --git a/src/pywinbox/_pywinbox_win.py b/src/pywinbox/_pywinbox_win.py
index d1c713b..4e40678 100644
--- a/src/pywinbox/_pywinbox_win.py
+++ b/src/pywinbox/_pywinbox_win.py
@@ -2,8 +2,15 @@
 from __future__ import annotations
 
 import sys
+if sys.platform != "win32":
+    raise OSError(f"Cannot import {__name__} on {sys.platform}")
+
+import ctypes
+
+from ._main import Box
 
 try:
+    # TypeAlias does not exist in typing for Python3.9
     from typing import TypeAlias
 except Exception:
     from typing import TYPE_CHECKING
@@ -11,13 +18,8 @@
         from typing_extensions import TypeAlias
 from typing import Union
 
-import ctypes
 import win32gui
 
-from ._main import Box
-
-assert sys.platform == "win32"
-
 
 # Thanks to poipoiPIO (https://github.com/poipoiPIO) for his HELP!!!
 try: