diff --git a/modules/config/system-path.nix b/modules/config/system-path.nix
index 80602468869..26685ae15f4 100644
--- a/modules/config/system-path.nix
+++ b/modules/config/system-path.nix
@@ -100,7 +100,7 @@ let
           # !!! Hacky, should modularise.
           postBuild =
             ''
-              if [ -x $out/bin/update-mime-database -a -d $out/share/mime/packages ]; then
+              if [ -x $out/bin/update-mime-database -a -w $out/share/mime/packages ]; then
                   $out/bin/update-mime-database -V $out/share/mime
               fi