diff --git a/src/archive/tar/common.go b/src/archive/tar/common.go
index b1704a402d..795bc0a916 100644
--- a/src/archive/tar/common.go
+++ b/src/archive/tar/common.go
@@ -85,14 +85,13 @@ func (h *Header) allowedFormats() (format int, paxHdrs map[string]string) {
 	format = formatUSTAR | formatPAX | formatGNU
 	paxHdrs = make(map[string]string)
 
-	verifyString := func(s string, size int, gnuLong bool, paxKey string) {
-
+	verifyString := func(s string, size int, paxKey string) {
 		// NUL-terminator is optional for path and linkpath.
 		// Technically, it is required for uname and gname,
 		// but neither GNU nor BSD tar checks for it.
 		tooLong := len(s) > size
-		if !isASCII(s) || (tooLong && !gnuLong) {
-			// TODO(dsnet): GNU supports UTF-8 (without NUL) for strings.
+		allowLongGNU := paxKey == paxPath || paxKey == paxLinkpath
+		if hasNUL(s) || (tooLong && !allowLongGNU) {
 			format &^= formatGNU // No GNU
 		}
 		if !isASCII(s) || tooLong {
@@ -120,15 +119,16 @@ func (h *Header) allowedFormats() (format int, paxHdrs map[string]string) {
 			}
 		}
 	}
-	verifyTime := func(ts time.Time, size int, ustarField bool, paxKey string) {
+	verifyTime := func(ts time.Time, size int, paxKey string) {
 		if ts.IsZero() {
 			return // Always okay
 		}
 		needsNano := ts.Nanosecond() != 0
+		hasFieldUSTAR := paxKey == paxMtime
 		if !fitsInBase256(size, ts.Unix()) || needsNano {
 			format &^= formatGNU // No GNU
 		}
-		if !fitsInOctal(size, ts.Unix()) || needsNano || !ustarField {
+		if !fitsInOctal(size, ts.Unix()) || needsNano || !hasFieldUSTAR {
 			format &^= formatUSTAR // No USTAR
 			if paxKey == paxNone {
 				format &^= formatPAX // No PAX
@@ -138,26 +138,23 @@ func (h *Header) allowedFormats() (format int, paxHdrs map[string]string) {
 		}
 	}
 
-	// TODO(dsnet): Add GNU long name support.
-	const supportGNULong = false
-
 	var blk block
 	v7 := blk.V7()
 	ustar := blk.USTAR()
 	gnu := blk.GNU()
-	verifyString(h.Name, len(v7.Name()), supportGNULong, paxPath)
-	verifyString(h.Linkname, len(v7.LinkName()), supportGNULong, paxLinkpath)
-	verifyString(h.Uname, len(ustar.UserName()), false, paxUname)
-	verifyString(h.Gname, len(ustar.GroupName()), false, paxGname)
+	verifyString(h.Name, len(v7.Name()), paxPath)
+	verifyString(h.Linkname, len(v7.LinkName()), paxLinkpath)
+	verifyString(h.Uname, len(ustar.UserName()), paxUname)
+	verifyString(h.Gname, len(ustar.GroupName()), paxGname)
 	verifyNumeric(h.Mode, len(v7.Mode()), paxNone)
 	verifyNumeric(int64(h.Uid), len(v7.UID()), paxUid)
 	verifyNumeric(int64(h.Gid), len(v7.GID()), paxGid)
 	verifyNumeric(h.Size, len(v7.Size()), paxSize)
 	verifyNumeric(h.Devmajor, len(ustar.DevMajor()), paxNone)
 	verifyNumeric(h.Devminor, len(ustar.DevMinor()), paxNone)
-	verifyTime(h.ModTime, len(v7.ModTime()), true, paxMtime)
-	verifyTime(h.AccessTime, len(gnu.AccessTime()), false, paxAtime)
-	verifyTime(h.ChangeTime, len(gnu.ChangeTime()), false, paxCtime)
+	verifyTime(h.ModTime, len(v7.ModTime()), paxMtime)
+	verifyTime(h.AccessTime, len(gnu.AccessTime()), paxAtime)
+	verifyTime(h.ChangeTime, len(gnu.ChangeTime()), paxCtime)
 
 	if !isHeaderOnlyType(h.Typeflag) && h.Size < 0 {
 		return formatUnknown, nil
diff --git a/src/archive/tar/reader_test.go b/src/archive/tar/reader_test.go
index 79d271717c..42d4ab7e14 100644
--- a/src/archive/tar/reader_test.go
+++ b/src/archive/tar/reader_test.go
@@ -350,6 +350,41 @@ func TestReader(t *testing.T) {
 			Uname:    "rawr",
 			Gname:    "dsnet",
 		}},
+	}, {
+		// This archive was generated by Writer but is readable by both
+		// GNU and BSD tar utilities.
+		// The archive generated by GNU is nearly byte-for-byte identical
+		// to the Go version except the Go version sets a negative Devminor
+		// just to force the GNU format.
+		file: "testdata/gnu-utf8.tar",
+		headers: []*Header{{
+			Name: "☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹",
+			Mode: 0644,
+			Uid:  1000, Gid: 1000,
+			ModTime:  time.Unix(0, 0),
+			Typeflag: '0',
+			Uname:    "☺",
+			Gname:    "⚹",
+			Devminor: -1,
+		}},
+	}, {
+		// This archive was generated by Writer but is readable by both
+		// GNU and BSD tar utilities.
+		// The archive generated by GNU is nearly byte-for-byte identical
+		// to the Go version except the Go version sets a negative Devminor
+		// just to force the GNU format.
+		file: "testdata/gnu-not-utf8.tar",
+		headers: []*Header{{
+			Name:     "hi\x80\x81\x82\x83bye",
+			Mode:     0644,
+			Uid:      1000,
+			Gid:      1000,
+			ModTime:  time.Unix(0, 0),
+			Typeflag: '0',
+			Uname:    "rawr",
+			Gname:    "dsnet",
+			Devminor: -1,
+		}},
 	}, {
 		// BSD tar v3.1.2 and GNU tar v1.27.1 both rejects PAX records
 		// with NULs in the key.
diff --git a/src/archive/tar/strconv.go b/src/archive/tar/strconv.go
index 89ac8112e5..e02963b74b 100644
--- a/src/archive/tar/strconv.go
+++ b/src/archive/tar/strconv.go
@@ -12,6 +12,11 @@ import (
 	"time"
 )
 
+// hasNUL reports whether the NUL character exists within s.
+func hasNUL(s string) bool {
+	return strings.IndexByte(s, 0) >= 0
+}
+
 // isASCII reports whether the input is an ASCII C-style string.
 func isASCII(s string) bool {
 	for _, c := range s {
@@ -59,7 +64,6 @@ func (f *formatter) formatString(b []byte, s string) {
 	if len(s) > len(b) {
 		f.err = ErrFieldTooLong
 	}
-	s = toASCII(s) // TODO(dsnet): Remove this for UTF-8 support in GNU format
 	copy(b, s)
 	if len(s) < len(b) {
 		b[len(s)] = 0
@@ -307,8 +311,8 @@ func validPAXRecord(k, v string) bool {
 	}
 	switch k {
 	case paxPath, paxLinkpath, paxUname, paxGname:
-		return strings.IndexByte(v, 0) < 0
+		return !hasNUL(v)
 	default:
-		return strings.IndexByte(k, 0) < 0
+		return !hasNUL(k)
 	}
 }
diff --git a/src/archive/tar/tar_test.go b/src/archive/tar/tar_test.go
index 22e23a6bbd..1a38ecb446 100644
--- a/src/archive/tar/tar_test.go
+++ b/src/archive/tar/tar_test.go
@@ -386,7 +386,7 @@ func TestHeaderAllowedFormats(t *testing.T) {
 		formats: formatUnknown,
 	}, {
 		header:  &Header{Name: "用戶名", Devmajor: -1 << 56},
-		formats: formatUnknown,
+		formats: formatGNU,
 	}, {
 		header:  &Header{Size: math.MaxInt64},
 		paxHdrs: map[string]string{paxSize: "9223372036854775807"},
@@ -408,10 +408,14 @@ func TestHeaderAllowedFormats(t *testing.T) {
 	}, {
 		header:  &Header{Name: strings.Repeat("a", nameSize)},
 		formats: formatUSTAR | formatPAX | formatGNU,
+	}, {
+		header:  &Header{Name: strings.Repeat("a", nameSize+1)},
+		paxHdrs: map[string]string{paxPath: strings.Repeat("a", nameSize+1)},
+		formats: formatPAX | formatGNU,
 	}, {
 		header:  &Header{Linkname: "用戶名"},
 		paxHdrs: map[string]string{paxLinkpath: "用戶名"},
-		formats: formatPAX,
+		formats: formatPAX | formatGNU,
 	}, {
 		header:  &Header{Linkname: strings.Repeat("用戶名\x00", nameSize)},
 		paxHdrs: map[string]string{paxLinkpath: strings.Repeat("用戶名\x00", nameSize)},
diff --git a/src/archive/tar/testdata/gnu-not-utf8.tar b/src/archive/tar/testdata/gnu-not-utf8.tar
new file mode 100644
index 0000000000..34b4c57771
Binary files /dev/null and b/src/archive/tar/testdata/gnu-not-utf8.tar differ
diff --git a/src/archive/tar/testdata/gnu-utf8.tar b/src/archive/tar/testdata/gnu-utf8.tar
new file mode 100644
index 0000000000..dde941c3ff
Binary files /dev/null and b/src/archive/tar/testdata/gnu-utf8.tar differ
diff --git a/src/archive/tar/writer.go b/src/archive/tar/writer.go
index a918ff3eef..ffef29af10 100644
--- a/src/archive/tar/writer.go
+++ b/src/archive/tar/writer.go
@@ -121,12 +121,10 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHdrs map[string]string) error {
 	}
 
 	// Pack the main header.
-	var f formatter
-	blk := tw.templateV7Plus(hdr, f.formatString, f.formatOctal)
+	var f formatter // Ignore errors since they are expected
+	fmtStr := func(b []byte, s string) { f.formatString(b, toASCII(s)) }
+	blk := tw.templateV7Plus(hdr, fmtStr, f.formatOctal)
 	blk.SetFormat(formatPAX)
-	if f.err != nil && len(paxHdrs) == 0 {
-		return f.err // Should never happen, otherwise PAX headers would be used
-	}
 	return tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag)
 }
 
@@ -134,10 +132,23 @@ func (tw *Writer) writeGNUHeader(hdr *Header) error {
 	// TODO(dsnet): Support writing sparse files.
 	// See https://golang.org/issue/13548
 
-	// TODO(dsnet): Support long filenames (with UTF-8) support.
+	// Use long-link files if Name or Linkname exceeds the field size.
+	const longName = "././@LongLink"
+	if len(hdr.Name) > nameSize {
+		data := hdr.Name + "\x00"
+		if err := tw.writeRawFile(longName, data, TypeGNULongName, formatGNU); err != nil {
+			return err
+		}
+	}
+	if len(hdr.Linkname) > nameSize {
+		data := hdr.Linkname + "\x00"
+		if err := tw.writeRawFile(longName, data, TypeGNULongLink, formatGNU); err != nil {
+			return err
+		}
+	}
 
 	// Pack the main header.
-	var f formatter
+	var f formatter // Ignore errors since they are expected
 	blk := tw.templateV7Plus(hdr, f.formatString, f.formatNumeric)
 	if !hdr.AccessTime.IsZero() {
 		f.formatNumeric(blk.GNU().AccessTime(), hdr.AccessTime.Unix())
@@ -146,9 +157,6 @@ func (tw *Writer) writeGNUHeader(hdr *Header) error {
 		f.formatNumeric(blk.GNU().ChangeTime(), hdr.ChangeTime.Unix())
 	}
 	blk.SetFormat(formatGNU)
-	if f.err != nil {
-		return f.err // Should never happen since header is validated
-	}
 	return tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag)
 }
 
diff --git a/src/archive/tar/writer_test.go b/src/archive/tar/writer_test.go
index a6eec5a9da..9d92ab89a6 100644
--- a/src/archive/tar/writer_test.go
+++ b/src/archive/tar/writer_test.go
@@ -219,6 +219,35 @@ func TestWriter(t *testing.T) {
 			},
 		}},
 		err: ErrHeader,
+	}, {
+		file: "testdata/gnu-utf8.tar",
+		entries: []*entry{{
+			header: &Header{
+				Name: "☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹",
+				Mode: 0644,
+				Uid:  1000, Gid: 1000,
+				ModTime:  time.Unix(0, 0),
+				Typeflag: '0',
+				Uname:    "☺",
+				Gname:    "⚹",
+				Devminor: -1, // Force use of GNU format
+			},
+		}},
+	}, {
+		file: "testdata/gnu-not-utf8.tar",
+		entries: []*entry{{
+			header: &Header{
+				Name:     "hi\x80\x81\x82\x83bye",
+				Mode:     0644,
+				Uid:      1000,
+				Gid:      1000,
+				ModTime:  time.Unix(0, 0),
+				Typeflag: '0',
+				Uname:    "rawr",
+				Gname:    "dsnet",
+				Devminor: -1, // Force use of GNU format
+			},
+		}},
 	}}
 
 	for _, v := range vectors {