diff --git a/externalsort/README.md b/externalsort/README.md
index 4e93e9d..51de944 100644
--- a/externalsort/README.md
+++ b/externalsort/README.md
@@ -14,15 +14,14 @@ type LineReader interface {
 	ReadLine() (string, error)
 }
 
-type LineWriterFlusher interface {
+type LineWriter interface {
 	Write(l string) error
-	Flush() error
 }
 ```
 и два конструктора:
 ```
 func NewReader(r io.Reader) LineReader
-func NewWriterFlusher(w io.Writer) LineWriterFlusher
+func NewWriter(w io.Writer) LineWriter
 ```
 
 `NewLineReader` оборачивает переданный `io.Reader` в `LineReader`.
@@ -38,7 +37,7 @@ func NewWriterFlusher(w io.Writer) LineWriterFlusher
 
 Функция слияния произвольного количества отсортированных групп строк:
 ```
-func Merge(w LineWriterFlusher, readers ...LineReader) error
+func Merge(w LineWriter, readers ...LineReader) error
 ```
 
 `Merge` по необходимости читает из reader'ов и пишет во writer.
diff --git a/externalsort/io.go b/externalsort/io.go
index 9867cb8..13f68ce 100644
--- a/externalsort/io.go
+++ b/externalsort/io.go
@@ -6,7 +6,6 @@ type LineReader interface {
 	ReadLine() (string, error)
 }
 
-type LineWriterFlusher interface {
+type LineWriter interface {
 	Write(l string) error
-	Flush() error
 }
diff --git a/externalsort/io_test.go b/externalsort/io_test.go
index 7ff8c19..7bcb91d 100644
--- a/externalsort/io_test.go
+++ b/externalsort/io_test.go
@@ -1,6 +1,7 @@
 package externalsort
 
 import (
+	"bufio"
 	"bytes"
 	"errors"
 	"io"
@@ -118,7 +119,7 @@ func TestLineReader_error(t *testing.T) {
 	require.True(t, errors.Is(err, io.EOF))
 }
 
-func TestLineWriterFlusher(t *testing.T) {
+func TestLineWriter(t *testing.T) {
 	for _, tc := range []struct {
 		name  string
 		lines []string
@@ -130,17 +131,25 @@ func TestLineWriterFlusher(t *testing.T) {
 			name:  "simple",
 			lines: []string{"a\n", "b\n", "c\n"},
 		},
+		{
+			name:  "large-line",
+			lines: []string{strings.Repeat("xx", 2049), "x", "y"},
+		},
+		{
+			name:  "huge-line",
+			lines: []string{strings.Repeat("?", 65537), "?", "!"},
+		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			var buf bytes.Buffer
-			w := NewWriterFlusher(&buf)
+			w := bufio.NewWriter(&buf)
+			lw := NewWriter(w)
 
 			for _, l := range tc.lines {
-				require.NoError(t, w.Write(l))
+				require.NoError(t, lw.Write(l))
 			}
 
 			require.NoError(t, w.Flush())
-
 			require.Equal(t, strings.Join(tc.lines, ""), buf.String())
 		})
 	}
diff --git a/externalsort/sort.go b/externalsort/sort.go
index 5760d49..170d925 100644
--- a/externalsort/sort.go
+++ b/externalsort/sort.go
@@ -10,11 +10,11 @@ func NewReader(r io.Reader) LineReader {
 	panic("implement me")
 }
 
-func NewWriterFlusher(w io.Writer) LineWriterFlusher {
+func NewWriter(w io.Writer) LineWriter {
 	panic("implement me")
 }
 
-func Merge(w LineWriterFlusher, readers ...LineReader) error {
+func Merge(w LineWriter, readers ...LineReader) error {
 	panic("implement me")
 }
 
diff --git a/externalsort/sort_test.go b/externalsort/sort_test.go
index 054dce1..6fac5b1 100644
--- a/externalsort/sort_test.go
+++ b/externalsort/sort_test.go
@@ -1,6 +1,7 @@
 package externalsort
 
 import (
+	"bufio"
 	"bytes"
 	"io/ioutil"
 	"path"
@@ -38,16 +39,18 @@ func TestMerge(t *testing.T) {
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			out := &bytes.Buffer{}
-			w := NewWriterFlusher(out)
+			w := bufio.NewWriter(out)
+			lw := NewWriter(w)
 
 			var readers []LineReader
 			for _, s := range tc.in {
 				readers = append(readers, newStringReader(s))
 			}
 
-			err := Merge(w, readers...)
+			err := Merge(lw, readers...)
 			require.NoError(t, err)
 
+			require.NoError(t, w.Flush())
 			require.Equal(t, tc.out, out.String())
 		})
 	}
@@ -85,12 +88,14 @@ func TestSort(t *testing.T) {
 			in, out := readTestCase(testCaseDir)
 
 			var buf bytes.Buffer
-			err := Sort(&buf, in...)
+			w := bufio.NewWriter(&buf)
+			err := Sort(w, in...)
 			require.NoError(t, err)
 
 			expected, err := ioutil.ReadFile(out)
 			require.NoError(t, err)
 
+			require.NoError(t, w.Flush())
 			require.Equal(t, string(expected), buf.String())
 		})
 	}