diff --git a/pkgs/development/libraries/libvirt/default.nix b/pkgs/development/libraries/libvirt/default.nix
index d5c6f1b6cf17..e83fd20e995f 100644
--- a/pkgs/development/libraries/libvirt/default.nix
+++ b/pkgs/development/libraries/libvirt/default.nix
@@ -352,11 +352,14 @@ stdenv.mkDerivation rec {
     substituteInPlace $out/bin/virt-xml-validate \
       --replace xmllint ${libxml2}/bin/xmllint
 
+    # Enable to set some options from the corresponding NixOS module (or other
+    # places) via environment variables.
     substituteInPlace $out/libexec/libvirt-guests.sh \
       --replace 'ON_BOOT="start"'       'ON_BOOT=''${ON_BOOT:-start}' \
       --replace 'ON_SHUTDOWN="suspend"' 'ON_SHUTDOWN=''${ON_SHUTDOWN:-suspend}' \
       --replace 'PARALLEL_SHUTDOWN=0'   'PARALLEL_SHUTDOWN=''${PARALLEL_SHUTDOWN:-0}' \
       --replace 'SHUTDOWN_TIMEOUT=300'  'SHUTDOWN_TIMEOUT=''${SHUTDOWN_TIMEOUT:-300}' \
+      --replace 'START_DELAY=0'         'START_DELAY=''${START_DELAY:-0}' \
       --replace "$out/bin"              '${gettext}/bin' \
       --replace 'lock/subsys'           'lock' \
       --replace 'gettext.sh'            'gettext.sh