diff --git a/encode.go b/encode.go
index 8354f2a..42a71c8 100644
--- a/encode.go
+++ b/encode.go
@@ -233,7 +233,7 @@ func writeValue(w io.Writer, value interface{}) error {
 }
 
 func needsQuotedValueRune(r rune) bool {
-	return r <= ' ' || r == '=' || r == '"' || r == utf8.RuneError
+	return r <= ' ' || r == '=' || r == '"' || r == 0x7f || r == utf8.RuneError
 }
 
 func writeStringValue(w io.Writer, value string, ok bool) error {
diff --git a/encode_test.go b/encode_test.go
index c3afdd2..29ef3c0 100644
--- a/encode_test.go
+++ b/encode_test.go
@@ -56,9 +56,12 @@ func TestEncodeKeyval(t *testing.T) {
 		{key: "k", value: "\xbd", want: `k="\ufffd"`},
 		{key: "k", value: "\ufffd\x00", want: `k="\ufffd\u0000"`},
 		{key: "k", value: "\ufffd", want: `k="\ufffd"`},
+		{key: "k", value: "\u007f", want: `k="\u007f"`},
+		{key: "k\u007f", value: "v", want: `k=v`},
 		{key: "k", value: []byte("\ufffd\x00"), want: `k="\ufffd\u0000"`},
 		{key: "k", value: []byte("\ufffd"), want: `k="\ufffd"`},
 		{key: "k", value: []byte("\u007f"), want: `k="\u007f"`},
+		{key: []byte("k\u007f"), value: "v", want: `k=v`},
 	}
 
 	for _, d := range data {
diff --git a/jsonstring.go b/jsonstring.go
index 030ac85..4550cb3 100644
--- a/jsonstring.go
+++ b/jsonstring.go
@@ -40,7 +40,7 @@ func writeQuotedString(w io.Writer, s string) (int, error) {
 	start := 0
 	for i := 0; i < len(s); {
 		if b := s[i]; b < utf8.RuneSelf {
-			if 0x20 <= b && b != '\\' && b != '"' {
+			if 0x20 <= b && b != '\\' && b != '"' && b != 0x7f {
 				i++
 				continue
 			}
@@ -91,14 +91,14 @@ func writeQuotedString(w io.Writer, s string) (int, error) {
 	return n, err
 }
 
-// NOTE: keep in sync with writeQuoteString above.
+// NOTE: keep in sync with writeQuotedString above.
 func writeQuotedBytes(w io.Writer, s []byte) (int, error) {
 	buf := getBuffer()
 	buf.WriteByte('"')
 	start := 0
 	for i := 0; i < len(s); {
 		if b := s[i]; b < utf8.RuneSelf {
-			if 0x20 <= b && b != '\\' && b != '"' {
+			if 0x20 <= b && b != '\\' && b != '"' && b != 0x7f {
 				i++
 				continue
 			}