diff --git a/src/encoding/pem/pem_test.go b/src/encoding/pem/pem_test.go
index c94b5ca53b5..56a7754b220 100644
--- a/src/encoding/pem/pem_test.go
+++ b/src/encoding/pem/pem_test.go
@@ -192,7 +192,7 @@ var lineBreakerTests = []lineBreakerTest{
 
 func TestLineBreaker(t *testing.T) {
 	for i, test := range lineBreakerTests {
-		buf := new(bytes.Buffer)
+		buf := new(strings.Builder)
 		var breaker lineBreaker
 		breaker.out = buf
 		_, err := breaker.Write([]byte(test.in))
@@ -206,13 +206,13 @@ func TestLineBreaker(t *testing.T) {
 			continue
 		}
 
-		if string(buf.Bytes()) != test.out {
-			t.Errorf("#%d: got:%s want:%s", i, string(buf.Bytes()), test.out)
+		if got := buf.String(); got != test.out {
+			t.Errorf("#%d: got:%s want:%s", i, got, test.out)
 		}
 	}
 
 	for i, test := range lineBreakerTests {
-		buf := new(bytes.Buffer)
+		buf := new(strings.Builder)
 		var breaker lineBreaker
 		breaker.out = buf
 
@@ -229,8 +229,8 @@ func TestLineBreaker(t *testing.T) {
 			continue
 		}
 
-		if string(buf.Bytes()) != test.out {
-			t.Errorf("#%d: (byte by byte) got:%s want:%s", i, string(buf.Bytes()), test.out)
+		if got := buf.String(); got != test.out {
+			t.Errorf("#%d: (byte by byte) got:%s want:%s", i, got, test.out)
 		}
 	}
 }
diff --git a/src/os/signal/signal_windows_test.go b/src/os/signal/signal_windows_test.go
index 9b145515726..02803e58080 100644
--- a/src/os/signal/signal_windows_test.go
+++ b/src/os/signal/signal_windows_test.go
@@ -5,11 +5,11 @@
 package signal
 
 import (
-	"bytes"
 	"internal/testenv"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"syscall"
 	"testing"
 	"time"
@@ -78,9 +78,9 @@ func main() {
 
 	// run it
 	cmd := exec.Command(exe)
-	var b bytes.Buffer
-	cmd.Stdout = &b
-	cmd.Stderr = &b
+	var buf strings.Builder
+	cmd.Stdout = &buf
+	cmd.Stderr = &buf
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		CreationFlags: syscall.CREATE_NEW_PROCESS_GROUP,
 	}
@@ -94,6 +94,6 @@ func main() {
 	}()
 	err = cmd.Wait()
 	if err != nil {
-		t.Fatalf("Program exited with error: %v\n%v", err, string(b.Bytes()))
+		t.Fatalf("Program exited with error: %v\n%v", err, buf.String())
 	}
 }
diff --git a/src/runtime/syscall_windows_test.go b/src/runtime/syscall_windows_test.go
index 37f8f40cfba..c0d3379e65a 100644
--- a/src/runtime/syscall_windows_test.go
+++ b/src/runtime/syscall_windows_test.go
@@ -5,7 +5,6 @@
 package runtime_test
 
 import (
-	"bytes"
 	"fmt"
 	"internal/abi"
 	"internal/syscall/windows/sysdll"
@@ -1044,7 +1043,7 @@ func TestNumCPU(t *testing.T) {
 
 	cmd := exec.Command(os.Args[0], "-test.run=TestNumCPU")
 	cmd.Env = append(os.Environ(), "GO_WANT_HELPER_PROCESS=1")
-	var buf bytes.Buffer
+	var buf strings.Builder
 	cmd.Stdout = &buf
 	cmd.Stderr = &buf
 	cmd.SysProcAttr = &syscall.SysProcAttr{CreationFlags: _CREATE_SUSPENDED}
@@ -1054,7 +1053,7 @@ func TestNumCPU(t *testing.T) {
 	}
 	defer func() {
 		err = cmd.Wait()
-		childOutput := string(buf.Bytes())
+		childOutput := buf.String()
 		if err != nil {
 			t.Fatalf("child failed: %v: %v", err, childOutput)
 		}