diff --git a/http/httpguts/httplex.go b/http/httpguts/httplex.go
index 6e071e8524..9b4de94019 100644
--- a/http/httpguts/httplex.go
+++ b/http/httpguts/httplex.go
@@ -12,7 +12,7 @@ import (
 	"golang.org/x/net/idna"
 )
 
-var isTokenTable = [127]bool{
+var isTokenTable = [256]bool{
 	'!':  true,
 	'#':  true,
 	'$':  true,
@@ -93,12 +93,7 @@ var isTokenTable = [127]bool{
 }
 
 func IsTokenRune(r rune) bool {
-	i := int(r)
-	return i < len(isTokenTable) && isTokenTable[i]
-}
-
-func isNotToken(r rune) bool {
-	return !IsTokenRune(r)
+	return r < utf8.RuneSelf && isTokenTable[byte(r)]
 }
 
 // HeaderValuesContainsToken reports whether any string in values
@@ -202,8 +197,8 @@ func ValidHeaderFieldName(v string) bool {
 	if len(v) == 0 {
 		return false
 	}
-	for _, r := range v {
-		if !IsTokenRune(r) {
+	for i := 0; i < len(v); i++ {
+		if !isTokenTable[v[i]] {
 			return false
 		}
 	}
diff --git a/http/httpguts/httplex_test.go b/http/httpguts/httplex_test.go
index a2c57f3927..791440b1a7 100644
--- a/http/httpguts/httplex_test.go
+++ b/http/httpguts/httplex_test.go
@@ -20,7 +20,7 @@ func isSeparator(c rune) bool {
 	return false
 }
 
-func TestIsToken(t *testing.T) {
+func TestIsTokenRune(t *testing.T) {
 	for i := 0; i <= 130; i++ {
 		r := rune(i)
 		expected := isChar(r) && !isCtl(r) && !isSeparator(r)
@@ -30,6 +30,15 @@ func TestIsToken(t *testing.T) {
 	}
 }
 
+func BenchmarkIsTokenRune(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		var r rune
+		for ; r < 1024; r++ {
+			IsTokenRune(r)
+		}
+	}
+}
+
 func TestHeaderValuesContainsToken(t *testing.T) {
 	tests := []struct {
 		vals  []string
@@ -100,6 +109,44 @@ func TestHeaderValuesContainsToken(t *testing.T) {
 	}
 }
 
+func TestValidHeaderFieldName(t *testing.T) {
+	tests := []struct {
+		in   string
+		want bool
+	}{
+		{"", false},
+		{"Accept Charset", false},
+		{"Accept-Charset", true},
+		{"AccepT-EncodinG", true},
+		{"CONNECTION", true},
+		{"résumé", false},
+	}
+	for _, tt := range tests {
+		got := ValidHeaderFieldName(tt.in)
+		if tt.want != got {
+			t.Errorf("ValidHeaderFieldName(%q) = %t; want %t", tt.in, got, tt.want)
+		}
+	}
+}
+
+func BenchmarkValidHeaderFieldName(b *testing.B) {
+	names := []string{
+		"",
+		"Accept Charset",
+		"Accept-Charset",
+		"AccepT-EncodinG",
+		"CONNECTION",
+		"résumé",
+	}
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for _, name := range names {
+			ValidHeaderFieldName(name)
+		}
+	}
+}
+
 func TestPunycodeHostPort(t *testing.T) {
 	tests := []struct {
 		in, want string