diff --git a/py_lib3mf/__init__.py b/py_lib3mf/__init__.py
index 13d3e7d..63420a9 100644
--- a/py_lib3mf/__init__.py
+++ b/py_lib3mf/__init__.py
@@ -12,7 +12,7 @@
 
 if system == "linux" and machine != "x86_64":
     raise OSError(f"Unsupported Machine Type: {machine}")
-elif system == "windows" and machine not in ("x86_64", "amd64")
+elif system == "windows" and machine not in ("x86_64", "amd64"):
     raise OSError(f"Unsupported Machine Type: {machine}")
 
 # skipping darwin machine check for now