new file mode 100644
--- /dev/null
+++ b/scripts/miscellaneous/private/__w2mpth__.m
@@ -0,0 +1,71 @@
+## Copyright (C) 2015 Philip Nienhuis
+##
+## This file is part of Octave.
+##
+## Octave is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or (at
+## your option) any later version.
+##
+## Octave is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*- 
+## @deftypefn {Function File} {@var{mingwpath} =} __w2mpth__ (@var{winpath})
+## Convert a Windows-style relative or full path name to MinGW style.
+##
+## @strong{Caution:} __w2mpth__ does not check the validity of the path.
+##
+## Examples:
+##
+## @example
+## @group
+##   mpth = __w2mpth ('D:\full\path\to\file.dat')
+##   @result{} '/D/full/path/to/file.dat'
+## @end group
+## @end example
+##
+## @example
+## @group
+##   mpth = __w2mpth ('relative\path\to\file.dat')
+##   @result{} 'relative/path/to/file.dat'
+## @end group
+## @end example
+##
+## @end deftypefn
+
+## Author: Philip Nienhuis <prnienhuis@users.sf.net>
+## Created: 2015-01-16
+
+function mingwpath = __w2mpth__ (winpath)
+
+  ## Check for platform
+  if (! ispc)
+    error ("__m2wpath__ should only be called on Windows platforms\n");
+  endif
+
+  ## Replace backslash file separators by forward slashes
+  mingwpath = strrep (winpath, '\', '/');
+  ## Also treat drive letter but beware of relative filenames
+  mingwpath = regexprep (mingwpath, '^([a-zA-Z]):', '/$1');
+
+endfunction
+
+
+## Use single quote strings for winpaths to cope with backslashes.
+%!test
+%! if (ispc)
+%!   assert (__w2mpth__ ('file.fil'), 'file.fil');
+%!   assert (__w2mpth__ ('\file.fil'), '/file.fil');
+%!   assert (__w2mpth__ ('G:\file.fil'), '/G/file.fil');
+%!   assert (__w2mpth__ ('r:\subdir\file.fil'), '/r/subdir/file.fil');
+%!   assert (__w2mpth__ ('relative\path\to\file.dat'),
+%!                       'relative/path/to/file.dat')
+%! endif
+

--- a/scripts/miscellaneous/tar.m
+++ b/scripts/miscellaneous/tar.m
@@ -55,6 +55,11 @@
 
   tarfile = make_absolute_filename (tarfile);
 
+  if (ispc)
+    ## Change tarfile into a mingw style acceptable for tar
+    tarfile = __w2mpth__ (tarfile);
+  endif
+
   cmd = sprintf ("tar cvf %s -C %s %s",
                           tarfile, rootdir, sprintf (" %s", files{:}));
 

--- a/scripts/miscellaneous/unpack.m
+++ b/scripts/miscellaneous/unpack.m
@@ -190,6 +190,11 @@
     nodotext = ext(ext != '.');
   endif
 
+  if (ispc && strcmp (nodotext, "tar"))
+    ## Change file pathname into a mingw style acceptable for tar
+    file = __w2mpth__ (file);
+  endif
+
   if (isfield (commandlist, tolower (nodotext)))
     [commandv, commandq, parsefcn, move] = deal (commandlist.(nodotext){:});
     origdir = pwd ();
@@ -198,8 +203,8 @@
     else
       startdir = origdir;
     endif
-    cstartdir = canonicalize_file_name (startdir);
-    cenddir = canonicalize_file_name (dir);
+    cstartdir = make_absolute_filename (startdir);
+    cenddir = make_absolute_filename (dir);
     needmove = move && ! strcmp (cstartdir, cenddir);
     if (nargout > 0 || needmove)
       command = commandv;