diff --git a/basis/io/streams/string/string.factor b/basis/io/streams/string/string.factor
index be9016d1f2..3a3815471a 100644
--- a/basis/io/streams/string/string.factor
+++ b/basis/io/streams/string/string.factor
@@ -8,10 +8,11 @@ IN: io.streams.string
 
 ! Readers
 TUPLE: string-reader { underlying string read-only } { i array-capacity } ;
+INSTANCE: string-reader noncopying-reader
 
 M: string-reader stream-element-type drop +character+ ;
-M: string-reader stream-read-partial stream-read ;
-M: string-reader stream-read sequence-read ;
+M: string-reader stream-read-partial-unsafe sequence-read-unsafe ;
+M: string-reader stream-read-unsafe sequence-read-unsafe ;
 M: string-reader stream-read1 sequence-read1 ;
 M: string-reader stream-read-until sequence-read-until ;
 M: string-reader stream-tell i>> ;
diff --git a/core/io/streams/byte-array/byte-array.factor b/core/io/streams/byte-array/byte-array.factor
index 6f9b05cf18..b917086206 100644
--- a/core/io/streams/byte-array/byte-array.factor
+++ b/core/io/streams/byte-array/byte-array.factor
@@ -15,11 +15,12 @@ M: byte-vector stream-element-type drop +byte+ ;
     dup encoder? [ stream>> ] when >byte-array ; inline
 
 TUPLE: byte-reader { underlying byte-array read-only } { i array-capacity } ;
+INSTANCE: byte-reader noncopying-reader
 
 M: byte-reader stream-element-type drop +byte+ ;
 
-M: byte-reader stream-read-partial stream-read ;
-M: byte-reader stream-read sequence-read ;
+M: byte-reader stream-read-partial-unsafe sequence-read-unsafe ;
+M: byte-reader stream-read-unsafe sequence-read-unsafe ;
 M: byte-reader stream-read1 sequence-read1 ;
 M: byte-reader stream-read-until sequence-read-until ;
 M: byte-reader dispose drop ;
diff --git a/core/io/streams/sequence/sequence.factor b/core/io/streams/sequence/sequence.factor
index 22882d6a24..47762628fe 100644
--- a/core/io/streams/sequence/sequence.factor
+++ b/core/io/streams/sequence/sequence.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2009 Daniel Ehrenberg
 ! See http://factorcode.org/license.txt for BSD license.
 USING: sequences io io.streams.plain kernel accessors math math.order
-growable destructors combinators ;
+growable destructors combinators sequences.private ;
 IN: io.streams.sequence
 
 ! Readers
@@ -17,26 +17,29 @@ SLOT: i
 : sequence-read1 ( stream -- elt/f )
     [ >sequence-stream< ?nth ] [ next ] bi ; inline
 
-: add-length ( n stream -- i+n )
-    [ i>> + ] [ underlying>> length ] bi min ; inline
+: (sequence-read-length) ( n buf stream -- buf count )
+    [ underlying>> length ] [ i>> ] bi - rot min ; inline
 
-: (sequence-read) ( n stream -- seq/f )
-    [ add-length ] keep
-    [ [ swap dup ] change-i drop ]
-    [ underlying>> ] bi
-    subseq ; inline
+: <sequence-copy> ( dest n i src -- n copy )
+    [ 0 ] 3curry dip <copy> ; inline
 
-: sequence-read ( n stream -- seq/f )
+: (sequence-read) ( n buf stream -- count )
+    [ (sequence-read-length) ]
+    [ [ dup pick + ] change-i underlying>> ] bi
+    [ <sequence-copy> (copy) drop ] 2curry keep ; inline
+
+: sequence-read-unsafe ( n buf stream -- count )
     dup >sequence-stream< bounds-check?
-    [ (sequence-read) ] [ 2drop f ] if ; inline
+    [ (sequence-read) ] [ 3drop 0 ] if ; inline
 
 : find-sep ( seps stream -- sep/f n )
     swap [ >sequence-stream< swap tail-slice ] dip
-    [ member-eq? ] curry find swap ; inline
+    [ member-eq? ] curry [ find swap ] curry keep
+    over [ drop ] [ nip length ] if ; inline
 
 : sequence-read-until ( separators stream -- seq sep/f )
     [ find-sep ] keep
-    [ sequence-read ] [ next ] bi swap ; inline
+    [ [ sequence-read-unsafe ] (read-into-new) ] [ next ] bi swap ; inline
 
 ! Writers
 M: growable dispose drop ;