diff --git a/setup.py b/setup.py
index e86667c..5fc1e35 100644
--- a/setup.py
+++ b/setup.py
@@ -2,6 +2,7 @@
 
 def extra_compile_args():
     """Returns extra compiler args for platform."""
+    import sys
     if sys.platform == 'win32':
         return ['/std:c++20', '/O2', '/DNDEBUG'] # for Visual Studio C++