diff --git a/src/pkg/exp/norm/input.go b/src/pkg/exp/norm/input.go
index ce159e9050..42e6f1b794 100644
--- a/src/pkg/exp/norm/input.go
+++ b/src/pkg/exp/norm/input.go
@@ -8,7 +8,7 @@ import "unicode/utf8"
 
 type input interface {
 	skipASCII(p int) int
-	skipNonStarter() int
+	skipNonStarter(p int) int
 	appendSlice(buf []byte, s, e int) []byte
 	copySlice(buf []byte, s, e int)
 	charinfo(p int) (uint16, int)
@@ -25,8 +25,7 @@ func (s inputString) skipASCII(p int) int {
 	return p
 }
 
-func (s inputString) skipNonStarter() int {
-	p := 0
+func (s inputString) skipNonStarter(p int) int {
 	for ; p < len(s) && !utf8.RuneStart(s[p]); p++ {
 	}
 	return p
@@ -71,8 +70,7 @@ func (s inputBytes) skipASCII(p int) int {
 	return p
 }
 
-func (s inputBytes) skipNonStarter() int {
-	p := 0
+func (s inputBytes) skipNonStarter(p int) int {
 	for ; p < len(s) && !utf8.RuneStart(s[p]); p++ {
 	}
 	return p
diff --git a/src/pkg/exp/norm/normalize.go b/src/pkg/exp/norm/normalize.go
index 25bb28d517..3bd40470d5 100644
--- a/src/pkg/exp/norm/normalize.go
+++ b/src/pkg/exp/norm/normalize.go
@@ -34,24 +34,28 @@ const (
 
 // Bytes returns f(b). May return b if f(b) = b.
 func (f Form) Bytes(b []byte) []byte {
-	n := f.QuickSpan(b)
+	rb := reorderBuffer{}
+	rb.init(f, b)
+	n := quickSpan(&rb, 0)
 	if n == len(b) {
 		return b
 	}
 	out := make([]byte, n, len(b))
 	copy(out, b[0:n])
-	return f.Append(out, b[n:]...)
+	return doAppend(&rb, out, n)
 }
 
 // String returns f(s).
 func (f Form) String(s string) string {
-	n := f.QuickSpanString(s)
+	rb := reorderBuffer{}
+	rb.initString(f, s)
+	n := quickSpan(&rb, 0)
 	if n == len(s) {
 		return s
 	}
-	out := make([]byte, 0, len(s))
+	out := make([]byte, n, len(s))
 	copy(out, s[0:n])
-	return string(f.AppendString(out, s[n:]))
+	return string(doAppend(&rb, out, n))
 }
 
 // IsNormal returns true if b == f(b).
@@ -122,23 +126,27 @@ func (f Form) IsNormalString(s string) bool {
 
 // patchTail fixes a case where a rune may be incorrectly normalized
 // if it is followed by illegal continuation bytes. It returns the
-// patched buffer and the number of trailing continuation bytes that
-// have been dropped.
-func patchTail(rb *reorderBuffer, buf []byte) ([]byte, int) {
+// patched buffer and whether there were trailing continuation bytes.
+func patchTail(rb *reorderBuffer, buf []byte) ([]byte, bool) {
 	info, p := lastRuneStart(&rb.f, buf)
 	if p == -1 || info.size == 0 {
-		return buf, 0
+		return buf, false
 	}
 	end := p + int(info.size)
 	extra := len(buf) - end
 	if extra > 0 {
+		// Potentially allocating memory. However, this only
+		// happens with ill-formed UTF-8.
+		x := make([]byte, 0)
+		x = append(x, buf[len(buf)-extra:]...)
 		buf = decomposeToLastBoundary(rb, buf[:end])
 		if rb.f.composing {
 			rb.compose()
 		}
-		return rb.flush(buf), extra
+		buf = rb.flush(buf)
+		return append(buf, x...), true
 	}
-	return buf, 0
+	return buf, false
 }
 
 func appendQuick(rb *reorderBuffer, dst []byte, i int) ([]byte, int) {
@@ -157,23 +165,23 @@ func (f Form) Append(out []byte, src ...byte) []byte {
 	}
 	rb := reorderBuffer{}
 	rb.init(f, src)
-	return doAppend(&rb, out)
+	return doAppend(&rb, out, 0)
 }
 
-func doAppend(rb *reorderBuffer, out []byte) []byte {
+func doAppend(rb *reorderBuffer, out []byte, p int) []byte {
 	src, n := rb.src, rb.nsrc
 	doMerge := len(out) > 0
-	p := 0
-	if p = src.skipNonStarter(); p > 0 {
+	if q := src.skipNonStarter(p); q > p {
 		// Move leading non-starters to destination.
-		out = src.appendSlice(out, 0, p)
-		buf, ndropped := patchTail(rb, out)
-		if ndropped > 0 {
-			out = src.appendSlice(buf, p-ndropped, p)
+		out = src.appendSlice(out, p, q)
+		buf, endsInError := patchTail(rb, out)
+		if endsInError {
+			out = buf
 			doMerge = false // no need to merge, ends with illegal UTF-8
 		} else {
 			out = decomposeToLastBoundary(rb, buf) // force decomposition
 		}
+		p = q
 	}
 	fd := &rb.f
 	if doMerge {
@@ -217,7 +225,7 @@ func (f Form) AppendString(out []byte, src string) []byte {
 	}
 	rb := reorderBuffer{}
 	rb.initString(f, src)
-	return doAppend(&rb, out)
+	return doAppend(&rb, out, 0)
 }
 
 // QuickSpan returns a boundary n such that b[0:n] == f(b[0:n]).
@@ -225,7 +233,8 @@ func (f Form) AppendString(out []byte, src string) []byte {
 func (f Form) QuickSpan(b []byte) int {
 	rb := reorderBuffer{}
 	rb.init(f, b)
-	return quickSpan(&rb, 0)
+	n := quickSpan(&rb, 0)
+	return n
 }
 
 func quickSpan(rb *reorderBuffer, i int) int {
@@ -301,7 +310,7 @@ func (f Form) FirstBoundary(b []byte) int {
 
 func firstBoundary(rb *reorderBuffer) int {
 	src, nsrc := rb.src, rb.nsrc
-	i := src.skipNonStarter()
+	i := src.skipNonStarter(0)
 	if i >= nsrc {
 		return -1
 	}
diff --git a/src/pkg/exp/norm/normalize_test.go b/src/pkg/exp/norm/normalize_test.go
index 6bd5292d3f..2e0c1f1712 100644
--- a/src/pkg/exp/norm/normalize_test.go
+++ b/src/pkg/exp/norm/normalize_test.go
@@ -253,7 +253,7 @@ var quickSpanNFDTests = []PositionTest{
 	{"\u0316\u0300cd", 6, ""},
 	{"\u043E\u0308b", 5, ""},
 	// incorrectly ordered combining characters
-	{"ab\u0300\u0316", 1, ""}, // TODO(mpvl): we could skip 'b' as well.
+	{"ab\u0300\u0316", 1, ""}, // TODO: we could skip 'b' as well.
 	{"ab\u0300\u0316cd", 1, ""},
 	// Hangul
 	{"같은", 0, ""},
@@ -465,6 +465,7 @@ var appendTests = []AppendTest{
 	{"\u0300", "\xFC\x80\x80\x80\x80\x80\u0300", "\u0300\xFC\x80\x80\x80\x80\x80\u0300"},
 	{"\xF8\x80\x80\x80\x80\u0300", "\u0300", "\xF8\x80\x80\x80\x80\u0300\u0300"},
 	{"\xFC\x80\x80\x80\x80\x80\u0300", "\u0300", "\xFC\x80\x80\x80\x80\x80\u0300\u0300"},
+	{"\xF8\x80\x80\x80", "\x80\u0300\u0300", "\xF8\x80\x80\x80\x80\u0300\u0300"},
 }
 
 func appendF(f Form, out []byte, s string) []byte {
@@ -475,9 +476,23 @@ func appendStringF(f Form, out []byte, s string) []byte {
 	return f.AppendString(out, s)
 }
 
+func bytesF(f Form, out []byte, s string) []byte {
+	buf := []byte{}
+	buf = append(buf, out...)
+	buf = append(buf, s...)
+	return f.Bytes(buf)
+}
+
+func stringF(f Form, out []byte, s string) []byte {
+	outs := string(out) + s
+	return []byte(f.String(outs))
+}
+
 func TestAppend(t *testing.T) {
 	runAppendTests(t, "TestAppend", NFKC, appendF, appendTests)
 	runAppendTests(t, "TestAppendString", NFKC, appendStringF, appendTests)
+	runAppendTests(t, "TestBytes", NFKC, bytesF, appendTests)
+	runAppendTests(t, "TestString", NFKC, stringF, appendTests)
 }
 
 func doFormBenchmark(b *testing.B, f Form, s string) {
diff --git a/src/pkg/exp/norm/readwriter.go b/src/pkg/exp/norm/readwriter.go
index ee58abd22d..2682894de0 100644
--- a/src/pkg/exp/norm/readwriter.go
+++ b/src/pkg/exp/norm/readwriter.go
@@ -27,7 +27,7 @@ func (w *normWriter) Write(data []byte) (n int, err error) {
 		}
 		w.rb.src = inputBytes(data[:m])
 		w.rb.nsrc = m
-		w.buf = doAppend(&w.rb, w.buf)
+		w.buf = doAppend(&w.rb, w.buf, 0)
 		data = data[m:]
 		n += m
 
@@ -101,7 +101,7 @@ func (r *normReader) Read(p []byte) (int, error) {
 		r.rb.src = inputBytes(r.inbuf[0:n])
 		r.rb.nsrc, r.err = n, err
 		if n > 0 {
-			r.outbuf = doAppend(&r.rb, r.outbuf)
+			r.outbuf = doAppend(&r.rb, r.outbuf, 0)
 		}
 		if err == io.EOF {
 			r.lastBoundary = len(r.outbuf)