diff --git a/modules/installer/tools/nixos-rebuild.sh b/modules/installer/tools/nixos-rebuild.sh
index 8d87b59bfb2..6ed294ebf64 100644
--- a/modules/installer/tools/nixos-rebuild.sh
+++ b/modules/installer/tools/nixos-rebuild.sh
@@ -81,9 +81,15 @@ while test "$#" -gt 0; do
       --show-trace|--no-build-hook|--keep-failed|-K|--keep-going|-k|--verbose|-v|--fallback)
         extraBuildFlags="$extraBuildFlags $i"
       ;;
-      --max-jobs|-j)
-        j="$1"; shift 1
-        extraBuildFlags="$extraBuildFlags $i $j"
+      --max-jobs|-j*)
+        if [ -z "${i:2}" ]; then
+          # -j n
+          extraBuildFlags="$extraBuildFlags $i $1"
+          shift 1
+        else
+          # -jn
+          extraBuildFlags="$extraBuildFlags $i"
+        fi
       ;;
       --fast)
         buildNix=