SILK and CELT mode are singular

doc/draft-ietf-codec-oggopus.xml

@@ -329,8 +329,8 @@ At 0.6 kbps, this is still a minimal bitrate impact over a naive, low quality
 </t>
 
 <t>
-Since medium-band audio is only supported in the SILK modes, wideband frames
- SHOULD be generated if switching from it to CELT modes, to ensure that
+Since medium-band audio is only supported in the SILK mode, wideband frames
+ SHOULD be generated if switching from it to CELT mode, to ensure that
  any PLC implementation that does try to migrate state between the modes
  will be able to preserve all of the available audio bandwidth.
 </t>