diff --git a/corepkgs/nar.nix b/corepkgs/nar.nix
index c3db19d0d3..04be17fb0c 100644
--- a/corepkgs/nar.nix
+++ b/corepkgs/nar.nix
@@ -8,7 +8,7 @@ let
 
       if [ $compressionType = xz ]; then
         ext=.xz
-        compressor="| ${xz} -9"
+        compressor="| ${xz} -7"
       elif [ $compressionType = bzip2 ]; then
         ext=.bz2
         compressor="| ${bzip2}"