diff --git a/src/os/exec/example_test.go b/src/os/exec/example_test.go
index bb166ceaf4..150f5cff48 100644
--- a/src/os/exec/example_test.go
+++ b/src/os/exec/example_test.go
@@ -5,7 +5,6 @@
 package exec_test
 
 import (
-	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -28,7 +27,7 @@ func ExampleLookPath() {
 func ExampleCommand() {
 	cmd := exec.Command("tr", "a-z", "A-Z")
 	cmd.Stdin = strings.NewReader("some input")
-	var out bytes.Buffer
+	var out strings.Builder
 	cmd.Stdout = &out
 	err := cmd.Run()
 	if err != nil {
diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
index 8f79b19eb6..52001bf9e3 100644
--- a/src/os/exec/exec_test.go
+++ b/src/os/exec/exec_test.go
@@ -804,7 +804,7 @@ func TestExtraFiles(t *testing.T) {
 	}
 
 	c = exec.CommandContext(ctx, exe)
-	var stdout, stderr bytes.Buffer
+	var stdout, stderr strings.Builder
 	c.Stdout = &stdout
 	c.Stderr = &stderr
 	c.ExtraFiles = []*os.File{tf}
@@ -822,7 +822,7 @@ func TestExtraFiles(t *testing.T) {
 	}
 	err = c.Run()
 	if err != nil {
-		t.Fatalf("Run: %v\n--- stdout:\n%s--- stderr:\n%s", err, stdout.Bytes(), stderr.Bytes())
+		t.Fatalf("Run: %v\n--- stdout:\n%s--- stderr:\n%s", err, stdout.String(), stderr.String())
 	}
 	if stdout.String() != text {
 		t.Errorf("got stdout %q, stderr %q; want %q on stdout", stdout.String(), stderr.String(), text)
@@ -904,7 +904,7 @@ func TestIgnorePipeErrorOnSuccess(t *testing.T) {
 	testWith := func(r io.Reader) func(*testing.T) {
 		return func(t *testing.T) {
 			cmd := helperCommand(t, "echo", "foo")
-			var out bytes.Buffer
+			var out strings.Builder
 			cmd.Stdin = r
 			cmd.Stdout = &out
 			if err := cmd.Run(); err != nil {
diff --git a/src/os/os_test.go b/src/os/os_test.go
index ea935d3295..3f75f28938 100644
--- a/src/os/os_test.go
+++ b/src/os/os_test.go
@@ -5,7 +5,6 @@
 package os_test
 
 import (
-	"bytes"
 	"errors"
 	"flag"
 	"fmt"
@@ -1167,7 +1166,7 @@ func exec(t *testing.T, dir, cmd string, args []string, expect string) {
 	}
 	w.Close()
 
-	var b bytes.Buffer
+	var b strings.Builder
 	io.Copy(&b, r)
 	output := b.String()
 
@@ -1718,7 +1717,7 @@ func runBinHostname(t *testing.T) string {
 	}
 	w.Close()
 
-	var b bytes.Buffer
+	var b strings.Builder
 	io.Copy(&b, r)
 	_, err = p.Wait()
 	if err != nil {