diff --git a/fossils.spec b/fossils.spec
index eab11a03772f3090fed77da261ce8cd2414e0e73..414b3617d16d95a6fcccac0eb896df424c07bd72 100644
--- a/fossils.spec
+++ b/fossils.spec
@@ -69,7 +69,7 @@ coll = COLLECT(
     a.zipfiles,
     a.datas,
     strip=False,
-    upx=True,
+    upx=False, # works well but slower runtime
     upx_exclude=[],
     name='fossils',
 )