diff --git a/nixos/lib/make-single-disk-zfs-image.nix b/nixos/lib/make-single-disk-zfs-image.nix
index a3564f9a8b68..585fa93b7fa0 100644
--- a/nixos/lib/make-single-disk-zfs-image.nix
+++ b/nixos/lib/make-single-disk-zfs-image.nix
@@ -21,6 +21,9 @@
 , # size of the FAT partition, in megabytes.
   bootSize ? 1024
 
+  , # memory allocated for virtualized build instance
+  memSize ? 1024
+
 , # The size of the root partition, in megabytes.
   rootSize ? 2048
 
@@ -230,7 +233,7 @@ let
   ).runInLinuxVM (
     pkgs.runCommand name
       {
-        memSize = 1024;
+        inherit memSize;
         QEMU_OPTS = "-drive file=$rootDiskImage,if=virtio,cache=unsafe,werror=report";
         preVM = ''
           PATH=$PATH:${pkgs.qemu_kvm}/bin
diff --git a/nixos/maintainers/scripts/openstack/openstack-image-zfs.nix b/nixos/maintainers/scripts/openstack/openstack-image-zfs.nix
index 936dcee12949..60f0535854dd 100644
--- a/nixos/maintainers/scripts/openstack/openstack-image-zfs.nix
+++ b/nixos/maintainers/scripts/openstack/openstack-image-zfs.nix
@@ -20,6 +20,12 @@ in
       default = "nixos-openstack-image-${config.system.nixos.label}-${pkgs.stdenv.hostPlatform.system}";
     };
 
+    ramMB = mkOption {
+      type = types.int;
+      default = 1024;
+      description = lib.mdDoc "RAM allocation for build VM";
+    };
+
     sizeMB = mkOption {
       type = types.int;
       default = 8192;
@@ -64,7 +70,7 @@ in
       includeChannel = copyChannel;
 
       bootSize = 1000;
-
+      memSize = cfg.ramMB;
       rootSize = cfg.sizeMB;
       rootPoolProperties = {
         ashift = 12;