diff --git a/v2v/convert_windows.ml b/v2v/convert_windows.ml
index 38fa300b2..f6f09114b 100644
--- a/v2v/convert_windows.ml
+++ b/v2v/convert_windows.ml
@@ -43,13 +43,6 @@ let convert ~keep_serial_console (g : G.guestfs) inspect source =
     try Sys.getenv "VIRT_TOOLS_DATA_DIR"
     with Not_found -> Guestfs_config.datadir // "virt-tools" in
 
-  let virtio_win =
-    try Sys.getenv "VIRTIO_WIN"
-    with Not_found ->
-      try Sys.getenv "VIRTIO_WIN_DIR" (* old name for VIRTIO_WIN *)
-      with Not_found ->
-        Guestfs_config.datadir // "virtio-win" in
-
   (* Check if RHEV-APT exists.  This is optional. *)
   let rhev_apt_exe = virt_tools_data_dir // "rhev-apt.exe" in
   let rhev_apt_exe =
@@ -289,7 +282,7 @@ if errorlevel 3010 exit /b 0
 
     disable_services root current_cs;
     disable_autoreboot root current_cs;
-    Windows_virtio.install_drivers g inspect systemroot virtio_win
+    Windows_virtio.install_drivers g inspect systemroot
                                    root current_cs
 
   and disable_services root current_cs =
diff --git a/v2v/windows_virtio.ml b/v2v/windows_virtio.ml
index 74411695c..bdce0387d 100644
--- a/v2v/windows_virtio.ml
+++ b/v2v/windows_virtio.ml
@@ -26,12 +26,19 @@ open Regedit
 open Types
 open Utils
 
-let rec install_drivers g inspect systemroot virtio_win root current_cs =
+let virtio_win =
+  try Sys.getenv "VIRTIO_WIN"
+  with Not_found ->
+    try Sys.getenv "VIRTIO_WIN_DIR" (* old name for VIRTIO_WIN *)
+    with Not_found ->
+      Guestfs_config.datadir // "virtio-win"
+
+let rec install_drivers g inspect systemroot root current_cs =
   (* Copy the virtio drivers to the guest. *)
   let driverdir = sprintf "%s/Drivers/VirtIO" systemroot in
   g#mkdir_p driverdir;
 
-  if not (copy_drivers g inspect virtio_win driverdir) then (
+  if not (copy_drivers g inspect driverdir) then (
     warning (f_"there are no virtio drivers available for this version of Windows (%d.%d %s %s).  virt-v2v looks for drivers in %s\n\nThe guest will be configured to use slower emulated devices.")
             inspect.i_major_version inspect.i_minor_version inspect.i_arch
             inspect.i_product_variant virtio_win;
@@ -349,7 +356,7 @@ and add_viostor_to_driver_database g root arch current_cs =
 (* Copy the matching drivers to the driverdir; return true if any have
  * been copied.
  *)
-and copy_drivers g inspect virtio_win driverdir =
+and copy_drivers g inspect driverdir =
   let ret = ref false in
   if is_directory virtio_win then (
     let cmd = sprintf "cd %s && find -type f" (quote virtio_win) in
diff --git a/v2v/windows_virtio.mli b/v2v/windows_virtio.mli
index 9edf4ec6b..2046faef5 100644
--- a/v2v/windows_virtio.mli
+++ b/v2v/windows_virtio.mli
@@ -19,13 +19,12 @@
 (** Functions for installing Windows virtio drivers. *)
 
 val install_drivers
-    : Guestfs.guestfs -> Types.inspect -> string -> string -> int64 -> string ->
+    : Guestfs.guestfs -> Types.inspect -> string -> int64 -> string ->
       Types.guestcaps_block_type * Types.guestcaps_net_type * Types.guestcaps_video_type
-(** [install_drivers g inspect systemroot virtio_win root current_cs]
+(** [install_drivers g inspect systemroot root current_cs]
     installs virtio drivers from the driver directory or driver
-    ISO ([virtio_win]) into the guest driver directory and updates
-    the registry so that the [viostor.sys] driver gets loaded by
-    Windows at boot.
+    ISO into the guest driver directory and updates the registry
+    so that the [viostor.sys] driver gets loaded by Windows at boot.
 
     [root] is the root node of the system hive (which is open for writes
     when this function is called).  [current_cs] is the name of the