diff --git a/distro/nix/greeter.nix b/distro/nix/greeter.nix
index c01d6cc9..e70e11b2 100644
--- a/distro/nix/greeter.nix
+++ b/distro/nix/greeter.nix
@@ -180,7 +180,9 @@ in
       fi
 
       if [ -f settings.json ]; then
-          if cp "$(${jq} -r '.customThemeFile' settings.json)" custom-theme.json; then
+          theme_file="$(${jq} -r '.customThemeFile // empty' settings.json)"
+          if [ -f "$theme_file" ] && [ -r "$theme_file" ]; then
+              cp "$theme_file" custom-theme.json
               mv settings.json settings.orig.json
               ${jq} '.customThemeFile = "${cacheDir}/custom-theme.json"' settings.orig.json > settings.json
           fi