diff --git a/doc/codecs.texi b/doc/codecs.texi
index 9a3a56d7dc..6093605d20 100644
--- a/doc/codecs.texi
+++ b/doc/codecs.texi
@@ -138,7 +138,8 @@ Set audio sampling rate (in Hz).
 Set number of audio channels.
 
 @item cutoff @var{integer} (@emph{encoding,audio})
-Set cutoff bandwidth.
+Set cutoff bandwidth. (Supported only by selected encoders, see
+their respective documentation sections.)
 
 @item frame_size @var{integer} (@emph{encoding,audio})
 Set audio frame size.
diff --git a/doc/encoders.texi b/doc/encoders.texi
index 5e311cb38a..8137465c76 100644
--- a/doc/encoders.texi
+++ b/doc/encoders.texi
@@ -488,6 +488,10 @@ is an optional AC-3 feature that increases quality by selectively encoding
 the left/right channels as mid/side. This option is enabled by default, and it
 is highly recommended that it be left as enabled except for testing purposes.
 
+@item cutoff @var{frequency}
+Set lowpass cutoff frequency. If unspecified, the encoder selects a default
+determined by various other encoding parameters.
+
 @end table
 
 @subsection Floating-Point-Only AC-3 Encoding Options