diff --git a/http/httphi/exchange_test.go b/http/httphi/exchange_test.go
index 1296556..ef69b66 100644
--- a/http/httphi/exchange_test.go
+++ b/http/httphi/exchange_test.go
@@ -1012,11 +1012,12 @@ func TestHandleBrowserSizedRequest(t *testing.T) {
 // connection go away. Either bound may be the one it ran into, and both are
 // reported to the caller.
 func TestHandleRequestTooLargeAnswers431(t *testing.T) {
-	request := "GET /echo HTTP/1.1\r\nHost: lneto.test\r\n"
-	for i := 0; i < 512; i++ {
-		request += "H" + strconv.Itoa(i) + ":v\r\n"
+	var request strings.Builder
+	request.WriteString("GET /echo HTTP/1.1\r\nHost: lneto.test\r\n")
+	for i := range 512 {
+		request.WriteString("H" + strconv.Itoa(i) + ":v\r\n")
 	}
-	request += "\r\n"
+	request.WriteString("\r\n")
 
 	for _, test := range []struct {
 		name    string
@@ -1046,7 +1047,7 @@ func TestHandleRequestTooLargeAnswers431(t *testing.T) {
 			var sm MuxSlice
 			sm.Reset(1)
 			sm.Handle("GET /echo", func(exch *Exchange) { served = true })
-			conn := newConn(request)
+			conn := newConn(request.String())
 			conn.Hangup()
 			exch := newExchange(t, conn, test.cfg)
 			err := Handle(exch, &sm, nopBackoff)
@@ -1065,8 +1066,8 @@ func TestHandleRequestTooLargeAnswers431(t *testing.T) {
 }
 
 func firstLine(s string) string {
-	if i := strings.Index(s, "\r\n"); i >= 0 {
-		return s[:i]
+	if before, _, ok := strings.Cut(s, "\r\n"); ok {
+		return before
 	}
 	return s
 }
diff --git a/http/httpraw/header_test.go b/http/httpraw/header_test.go
index c7cf12f..1ac6288 100644
--- a/http/httpraw/header_test.go
+++ b/http/httpraw/header_test.go
@@ -609,15 +609,16 @@ func TestHeader_SetIntNoAlloc(t *testing.T) {
 // exceeds.
 func TestHeader_FieldTableSizedFromBuffer(t *testing.T) {
 	const wantVal = "the-canary-value"
-	raw := "GET / HTTP/1.1\r\nHost: lneto.test\r\n"
-	for i := 0; i < 40; i++ {
-		raw += "X-Field-" + strconv.Itoa(i) + ": value-of-a-realistic-length-here\r\n"
+	var raw strings.Builder
+	raw.WriteString("GET / HTTP/1.1\r\nHost: lneto.test\r\n")
+	for i := range 40 {
+		raw.WriteString("X-Field-" + strconv.Itoa(i) + ": value-of-a-realistic-length-here\r\n")
 	}
-	raw += "X-Canary: " + wantVal + "\r\n\r\n"
+	raw.WriteString("X-Canary: " + wantVal + "\r\n\r\n")
 
 	var h Header
 	h.Reset(make([]byte, 0, 8192), numHeaderCapacity) // Room for the block with plenty to spare.
-	err := h.ParseBytes(false, []byte(raw))
+	err := h.ParseBytes(false, []byte(raw.String()))
 	if err != nil {
 		t.Fatalf("parsing a 42 field request into an 8kB buffer: %s", err)
 	}
@@ -629,15 +630,16 @@ func TestHeader_FieldTableSizedFromBuffer(t *testing.T) {
 // A buffer too small for the fields it is handed must be refused with an error
 // the caller can act on, so a server answers 431 instead of dropping the peer.
 func TestHeader_FieldTableFullIsReported(t *testing.T) {
-	raw := "GET / HTTP/1.1\r\n"
-	for i := 0; i < 64; i++ {
-		raw += "H" + strconv.Itoa(i) + ":v\r\n" // As short as a field gets.
+	var raw strings.Builder
+	raw.WriteString("GET / HTTP/1.1\r\n")
+	for i := range 64 {
+		raw.WriteString("H" + strconv.Itoa(i) + ":v\r\n") // As short as a field gets.
 	}
-	raw += "\r\n"
+	raw.WriteString("\r\n")
 	var h Header
 	h.Reset(make([]byte, 0, 512), numHeaderCapacity)
 	h.ConfigBufferGrowth(false)
-	err := h.ParseBytes(false, []byte(raw))
+	err := h.ParseBytes(false, []byte(raw.String()))
 	if !errors.Is(err, ErrHeaderTooMany) {
 		t.Fatalf("want ErrHeaderFieldsTooLarge, got %v", err)
 	}