diff --git a/basis/io/streams/duplex/duplex-docs.factor b/basis/io/streams/duplex/duplex-docs.factor
index 48afafeec7..5bf33e9002 100644
--- a/basis/io/streams/duplex/duplex-docs.factor
+++ b/basis/io/streams/duplex/duplex-docs.factor
@@ -20,11 +20,11 @@ HELP: <duplex-stream>
 
 HELP: with-stream
 { $values { "stream" duplex-stream } { "quot" quotation } }
-{ $description "Calls the quotation in a new dynamic scope, with both " { $link input-stream } " and " { $link output-stream } " rebound to  " { $snippet "stream" } ". The stream is closed if the quotation returns or throws an error." } ;
+{ $description "Calls the quotation in a new dynamic scope, with both " { $link input-stream } " and " { $link output-stream } " rebound to " { $snippet "stream" } ", which must be a duplex stream. The stream is closed if the quotation returns or throws an error." } ;
 
 HELP: with-stream*
 { $values { "stream" duplex-stream } { "quot" quotation } }
-{ $description "Calls the quotation in a new dynamic scope, with both " { $link input-stream } " and " { $link output-stream } " rebound to  " { $snippet "stream" } "." }
+{ $description "Calls the quotation in a new dynamic scope, with both " { $link input-stream } " and " { $link output-stream } " rebound to " { $snippet "stream" } ", which must be a duplex stream." }
 { $notes "This word does not close the stream. Compare with " { $link with-stream } "." } ;
 
 HELP: <encoder-duplex>