diff --git a/src/mime/mediatype.go b/src/mime/mediatype.go
index 05390773a8..56ceb48853 100644
--- a/src/mime/mediatype.go
+++ b/src/mime/mediatype.go
@@ -19,7 +19,7 @@ import (
 // FormatMediaType returns the empty string.
 func FormatMediaType(t string, param map[string]string) string {
 	var b strings.Builder
-	if slash := strings.Index(t, "/"); slash == -1 {
+	if slash := strings.IndexByte(t, '/'); slash == -1 {
 		if !isToken(t) {
 			return ""
 		}
@@ -48,7 +48,38 @@ func FormatMediaType(t string, param map[string]string) string {
 			return ""
 		}
 		b.WriteString(strings.ToLower(attribute))
+
+		needEnc := needsEncoding(value)
+		if needEnc {
+			// RFC 2231 section 4
+			b.WriteByte('*')
+		}
 		b.WriteByte('=')
+
+		if needEnc {
+			b.WriteString("utf-8''")
+
+			offset := 0
+			for index := 0; index < len(value); index++ {
+				ch := value[index]
+				// {RFC 2231 section 7}
+				// attribute-char := <any (US-ASCII) CHAR except SPACE, CTLs, "*", "'", "%", or tspecials>
+				if ch <= ' ' || ch >= 0x7F ||
+					ch == '*' || ch == '\'' || ch == '%' ||
+					isTSpecial(rune(ch)) {
+
+					b.WriteString(value[offset:index])
+					offset = index + 1
+
+					b.WriteByte('%')
+					b.WriteByte(upperhex[ch>>4])
+					b.WriteByte(upperhex[ch&0x0F])
+				}
+			}
+			b.WriteString(value[offset:])
+			continue
+		}
+
 		if isToken(value) {
 			b.WriteString(value)
 			continue
@@ -63,9 +94,6 @@ func FormatMediaType(t string, param map[string]string) string {
 				offset = index
 				b.WriteByte('\\')
 			}
-			if character&0x80 != 0 {
-				return ""
-			}
 		}
 		b.WriteString(value[offset:])
 		b.WriteByte('"')
diff --git a/src/mime/mediatype_test.go b/src/mime/mediatype_test.go
index 945a8189e1..e91ff38d68 100644
--- a/src/mime/mediatype_test.go
+++ b/src/mime/mediatype_test.go
@@ -6,6 +6,7 @@ package mime
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 )
 
@@ -481,8 +482,9 @@ var formatTests = []formatTest{
 	{"noslash", map[string]string{"X": "Y"}, "noslash; x=Y"}, // e.g. Content-Disposition values (RFC 2183); issue 11289
 	{"foo bar/baz", nil, ""},
 	{"foo/bar baz", nil, ""},
-	{"attachment", map[string]string{"filename": "ĄĄŽŽČČŠŠ"}, ""},
-	{"attachment", map[string]string{"filename": "ÁÁÊÊÇÇÎÎ"}, ""},
+	{"attachment", map[string]string{"filename": "ĄĄŽŽČČŠŠ"}, "attachment; filename*=utf-8''%C4%84%C4%84%C5%BD%C5%BD%C4%8C%C4%8C%C5%A0%C5%A0"},
+	{"attachment", map[string]string{"filename": "ÁÁÊÊÇÇÎÎ"}, "attachment; filename*=utf-8''%C3%81%C3%81%C3%8A%C3%8A%C3%87%C3%87%C3%8E%C3%8E"},
+	{"attachment", map[string]string{"filename": "数据统计.png"}, "attachment; filename*=utf-8''%E6%95%B0%E6%8D%AE%E7%BB%9F%E8%AE%A1.png"},
 	{"foo/BAR", nil, "foo/bar"},
 	{"foo/BAR", map[string]string{"X": "Y"}, "foo/bar; x=Y"},
 	{"foo/BAR", map[string]string{"space": "With space"}, `foo/bar; space="With space"`},
@@ -491,7 +493,8 @@ var formatTests = []formatTest{
 	{"foo/BAR", map[string]string{"both": `With \backslash and "quote`}, `foo/bar; both="With \\backslash and \"quote"`},
 	{"foo/BAR", map[string]string{"": "empty attribute"}, ""},
 	{"foo/BAR", map[string]string{"bad attribute": "baz"}, ""},
-	{"foo/BAR", map[string]string{"nonascii": "not an ascii character: ä"}, ""},
+	{"foo/BAR", map[string]string{"nonascii": "not an ascii character: ä"}, "foo/bar; nonascii*=utf-8''not%20an%20ascii%20character%3A%20%C3%A4"},
+	{"foo/BAR", map[string]string{"ctl": "newline: \n nil: \000"}, "foo/bar; ctl*=utf-8''newline%3A%20%0A%20nil%3A%20%00"},
 	{"foo/bar", map[string]string{"a": "av", "b": "bv", "c": "cv"}, "foo/bar; a=av; b=bv; c=cv"},
 	{"foo/bar", map[string]string{"0": "'", "9": "'"}, "foo/bar; 0='; 9='"},
 	{"foo", map[string]string{"bar": ""}, `foo; bar=""`},
@@ -503,5 +506,21 @@ func TestFormatMediaType(t *testing.T) {
 		if got != tt.want {
 			t.Errorf("%d. FormatMediaType(%q, %v) = %q; want %q", i, tt.typ, tt.params, got, tt.want)
 		}
+		if got == "" {
+			continue
+		}
+		typ, params, err := ParseMediaType(got)
+		if err != nil {
+			t.Errorf("%d. ParseMediaType(%q) err: %v", i, got, err)
+		}
+		if typ != strings.ToLower(tt.typ) {
+			t.Errorf("%d. ParseMediaType(%q) typ = %q; want %q", i, got, typ, tt.typ)
+		}
+		for k, v := range tt.params {
+			k = strings.ToLower(k)
+			if params[k] != v {
+				t.Errorf("%d. ParseMediaType(%q) params[%s] = %q; want %q", i, got, k, params[k], v)
+			}
+		}
 	}
 }