diff --git a/beetsplug/convert.py b/beetsplug/convert.py
index de91604f5..8c7f20e4d 100644
--- a/beetsplug/convert.py
+++ b/beetsplug/convert.py
@@ -199,9 +199,10 @@ class ConvertPlugin(BeetsPlugin):
             # Something went wrong (probably Ctrl+C), remove temporary files
             self._log.info(u'Encoding {0} failed. Cleaning up...',
                            util.displayable_path(source))
-            self._log.debug(u'Command {0} exited with status {1}',
-                            exc.cmd.decode('utf8', 'ignore'),
-                            exc.returncode)
+            self._log.debug(u'Command {0} exited with status {1}: {2}',
+                            args,
+                            exc.returncode,
+                            exc.output)
             util.remove(dest)
             util.prune_dirs(os.path.dirname(dest))
             raise
diff --git a/test/test_convert.py b/test/test_convert.py
index 886614822..ef37466d7 100644
--- a/test/test_convert.py
+++ b/test/test_convert.py
@@ -35,10 +35,12 @@ class TestHelper(helper.TestHelper):
         if re.search('[^a-zA-Z0-9]', tag):
             raise ValueError(u"tag '{0}' must only contain letters and digits"
                              .format(tag))
-        # FIXME This is not portable. For windows we need to use our own
-        # python script that performs the same task.
-        return u'sh -c "cp \'$source\' \'$dest\'; ' \
-               u'printf {0} >> \'$dest\'"'.format(tag)
+
+        # A Python script that copies the file and appends a tag.
+        return u'python -c \'import sys; inf = open(sys.argv[1], "rb"); ' \
+               u'outf = open(sys.argv[2], "wb"); ' \
+               u'outf.write(inf.read()); ' \
+               u'outf.write(b"{}")\' $source $dest'.format(tag)
 
     def assertFileTag(self, path, tag):  # noqa
         """Assert that the path is a file and the files content ends with `tag`.