diff --git a/scripts/MediaHive.spec b/scripts/MediaHive.spec
index 30ae419..9d36c6f 100644
--- a/scripts/MediaHive.spec
+++ b/scripts/MediaHive.spec
@@ -123,6 +123,11 @@ exe = EXE(
     windowed=True,
 )
 
+# UPX breaks .NET assemblies: packing Python.Runtime.dll strips/corrupts its
+# CLR metadata and pythonnet then fails with "Failed to resolve
+# Python.Runtime.Loader.Initialize from .../Python.Runtime.dll".
+_upx_exclude = ["Python.Runtime.dll"] if sys.platform == "win32" else []
+
 coll = COLLECT(
     exe,
     a.binaries,
@@ -130,7 +135,7 @@ coll = COLLECT(
     a.datas,
     strip=False,
     upx=True,
-    upx_exclude=[],
+    upx_exclude=_upx_exclude,
     name="MediaHive",
 )