diff --git a/pkgs/applications/virtualization/xen/generic/default.nix b/pkgs/applications/virtualization/xen/generic/default.nix
index a59c2f5aea06..32b9c5406046 100644
--- a/pkgs/applications/virtualization/xen/generic/default.nix
+++ b/pkgs/applications/virtualization/xen/generic/default.nix
@@ -342,7 +342,9 @@ stdenv.mkDerivation (finalAttrs: {
     ++ lib.lists.optional withInternalOVMF "--enable-ovmf"
 
     ++ lib.lists.optional withIPXE "--with-system-ipxe=${ipxe}"
-    ++ lib.lists.optional withInternalIPXE "--enable-ipxe";
+    ++ lib.lists.optional withInternalIPXE "--enable-ipxe"
+
+    ++ lib.lists.optional withFlask "--enable-xsmpolicy";
 
   makeFlags =
     [