diff --git a/src/cmd/cover/cover_test.go b/src/cmd/cover/cover_test.go
index 28be231121..d9d63e4587 100644
--- a/src/cmd/cover/cover_test.go
+++ b/src/cmd/cover/cover_test.go
@@ -400,7 +400,7 @@ func TestCoverHTML(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	var out bytes.Buffer
+	var out strings.Builder
 	scan := bufio.NewScanner(bytes.NewReader(entireHTML))
 	in := false
 	for scan.Scan() {
diff --git a/src/cmd/cover/html.go b/src/cmd/cover/html.go
index 3c1d17e7b9..400a7d879d 100644
--- a/src/cmd/cover/html.go
+++ b/src/cmd/cover/html.go
@@ -6,7 +6,6 @@ package main
 
 import (
 	"bufio"
-	"bytes"
 	"cmd/internal/browser"
 	"fmt"
 	"html/template"
@@ -157,7 +156,7 @@ func rgb(n int) string {
 
 // colors generates the CSS rules for coverage colors.
 func colors() template.CSS {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	for i := 0; i < 11; i++ {
 		fmt.Fprintf(&buf, ".cov%v { color: %v }\n", i, rgb(i))
 	}