diff --git a/beetsplug/convert.py b/beetsplug/convert.py
index f11204924..9debd6ca1 100644
--- a/beetsplug/convert.py
+++ b/beetsplug/convert.py
@@ -60,10 +60,10 @@ def get_format(fmt=None):
     try:
         format_info = config['convert']['formats'][fmt].get(dict)
         command = format_info['command']
-        extension = format_info['extension']
+        extension = format_info.get('extension', fmt)
     except KeyError:
         raise ui.UserError(
-            u'convert: format {0} needs "command" and "extension" fields'
+            u'convert: format {0} needs the "command" field'
             .format(fmt)
         )
     except ConfigTypeError:
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 31cd892f7..251057c20 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -8,6 +8,7 @@ New features:
 
 * :doc:`/plugins/convert`: A new `album_art_maxwidth` lets you resize album
   art while copying it.
+* :doc:`/plugins/convert`: Make `extension` optional for conversion formats.
 * :doc:`/plugins/importadded`: A new `preserve_write_mtimes` option
   lets you preserve mtime of files after each write.
 * :doc:`/plugins/lyrics`: The plugin can now translate the fetched lyrics to a
diff --git a/docs/plugins/convert.rst b/docs/plugins/convert.rst
index f5b258065..f2f28c63d 100644
--- a/docs/plugins/convert.rst
+++ b/docs/plugins/convert.rst
@@ -113,12 +113,12 @@ default. To convert the audio to `wav`, run ``beet convert -f wav``.
 This will also use the format key (`wav`) as the file extension.
 
 Each entry in the ``formats`` map consists of a key (the name of the
-format) as well as the command and the possibly the file extension.
+format) as well as the command and optionally the file extension.
 ``extension`` is the filename extension to be used for newly transcoded
-files.  If only the command is given as a string, the file extension
-defaults to the format's name. ``command`` is the command-line to use
-to transcode audio. The tokens ``$source`` and ``$dest`` in the command
-are replaced with the paths to the existing and new file.
+files.  If only the command is given as a string or the extension is not
+provided, the file extension defaults to the format's name. ``command`` is the
+command to use to transcode audio. The tokens ``$source`` and ``$dest`` in the
+command are replaced with the paths to the existing and new file.
 
 The plugin in comes with default commands for the most common audio
 formats: `mp3`, `alac`, `flac`, `aac`, `opus`, `ogg`, `wmv`. For