diff --git a/src/proxy/build_pythoncore.py b/src/proxy/build_pythoncore.py
index 481dec5..ecc857f 100644
--- a/src/proxy/build_pythoncore.py
+++ b/src/proxy/build_pythoncore.py
@@ -4,7 +4,7 @@
 
 _EXCLUDE_MODULES = ["ensurepip", "idlelib", "test", "tkinter", "turtle_demo", "venv"]
 
-libdir = Path(sys.executable).parent.joinpath("Lib")
+libdir = Path(sys.base_prefix).joinpath("Lib")
 assert libdir.exists()
 
 with zipfile.PyZipFile(sys.argv[1], optimize=2, mode="w") as fp:
@@ -12,3 +12,4 @@
     for path in libdir.iterdir():
         if path.is_dir() and path.name not in _EXCLUDE_MODULES:
             fp.writepy(path)  # pyright: ignore[reportArgumentType]
+    assert fp.namelist(), "Generated pythoncore.zip is empty. This will not block the build but will break MO2 at runtime!"