diff --git a/terminal.go b/terminal.go
index bb69c5b..a0ddba3 100644
--- a/terminal.go
+++ b/terminal.go
@@ -7,6 +7,7 @@
 import (
 	"io"
 	"sync"
+	"unicode/utf8"
 )
 
 // EscapeCodes contains escape sequences that can be written to the terminal in
@@ -35,11 +36,12 @@
 // Terminal contains the state for running a VT100 terminal that is capable of
 // reading lines of input.
 type Terminal struct {
-	// AutoCompleteCallback, if non-null, is called for each keypress
-	// with the full input line and the current position of the cursor.
-	// If it returns a nil newLine, the key press is processed normally.
-	// Otherwise it returns a replacement line and the new cursor position.
-	AutoCompleteCallback func(line []byte, pos, key int) (newLine []byte, newPos int)
+	// AutoCompleteCallback, if non-null, is called for each keypress with
+	// the full input line and the current position of the cursor (in
+	// bytes, as an index into |line|). If it returns ok=false, the key
+	// press is processed normally. Otherwise it returns a replacement line
+	// and the new cursor position.
+	AutoCompleteCallback func(line string, pos int, key rune) (newLine string, newPos int, ok bool)
 
 	// Escape contains a pointer to the escape codes for this terminal.
 	// It's always a valid pointer, although the escape codes themselves
@@ -54,7 +56,7 @@
 	prompt string
 
 	// line is the current line being entered.
-	line []byte
+	line []rune
 	// pos is the logical position of the cursor in line
 	pos int
 	// echo is true if local echo is enabled
@@ -109,7 +111,7 @@
 	keyEnter     = '\r'
 	keyEscape    = 27
 	keyBackspace = 127
-	keyUnknown   = 256 + iota
+	keyUnknown   = 0xd800 /* UTF-16 surrogate area */ + iota
 	keyUp
 	keyDown
 	keyLeft
@@ -123,10 +125,10 @@
 )
 
 // bytesToKey tries to parse a key sequence from b. If successful, it returns
-// the key and the remainder of the input. Otherwise it returns -1.
-func bytesToKey(b []byte) (int, []byte) {
+// the key and the remainder of the input. Otherwise it returns utf8.RuneError.
+func bytesToKey(b []byte) (rune, []byte) {
 	if len(b) == 0 {
-		return -1, nil
+		return utf8.RuneError, nil
 	}
 
 	switch b[0] {
@@ -139,7 +141,11 @@
 	}
 
 	if b[0] != keyEscape {
-		return int(b[0]), b[1:]
+		if !utf8.FullRune(b) {
+			return utf8.RuneError, b
+		}
+		r, l := utf8.DecodeRune(b)
+		return r, b[l:]
 	}
 
 	if len(b) >= 3 && b[0] == keyEscape && b[1] == '[' {
@@ -183,19 +189,20 @@
 		}
 	}
 
-	return -1, b
+	return utf8.RuneError, b
 }
 
 // queue appends data to the end of t.outBuf
-func (t *Terminal) queue(data []byte) {
-	t.outBuf = append(t.outBuf, data...)
+func (t *Terminal) queue(data []rune) {
+	t.outBuf = append(t.outBuf, []byte(string(data))...)
 }
 
-var eraseUnderCursor = []byte{' ', keyEscape, '[', 'D'}
-var space = []byte{' '}
+var eraseUnderCursor = []rune{' ', keyEscape, '[', 'D'}
+var space = []rune{' '}
 
-func isPrintable(key int) bool {
-	return key >= 32 && key < 127
+func isPrintable(key rune) bool {
+	isInSurrogateArea := key >= 0xd800 && key <= 0xdbff
+	return key >= 32 && !isInSurrogateArea
 }
 
 // moveCursorToPos appends data to t.outBuf which will move the cursor to the
@@ -235,7 +242,7 @@
 }
 
 func (t *Terminal) move(up, down, left, right int) {
-	movement := make([]byte, 3*(up+down+left+right))
+	movement := make([]rune, 3*(up+down+left+right))
 	m := movement
 	for i := 0; i < up; i++ {
 		m[0] = keyEscape
@@ -266,13 +273,13 @@
 }
 
 func (t *Terminal) clearLineToRight() {
-	op := []byte{keyEscape, '[', 'K'}
+	op := []rune{keyEscape, '[', 'K'}
 	t.queue(op)
 }
 
 const maxLineLength = 4096
 
-func (t *Terminal) setLine(newLine []byte, newPos int) {
+func (t *Terminal) setLine(newLine []rune, newPos int) {
 	if t.echo {
 		t.moveCursorToPos(0)
 		t.writeLine(newLine)
@@ -354,7 +361,7 @@
 
 // handleKey processes the given key and, optionally, returns a line of text
 // that the user has entered.
-func (t *Terminal) handleKey(key int) (line string, ok bool) {
+func (t *Terminal) handleKey(key rune) (line string, ok bool) {
 	switch key {
 	case keyBackspace:
 		if t.pos == 0 {
@@ -402,24 +409,24 @@
 			t.historyPending = string(t.line)
 		}
 		t.historyIndex++
-		t.setLine([]byte(entry), len(entry))
+		t.setLine([]rune(entry), len(entry))
 	case keyDown:
 		switch t.historyIndex {
 		case -1:
 			return
 		case 0:
-			t.setLine([]byte(t.historyPending), len(t.historyPending))
+			t.setLine([]rune(t.historyPending), len(t.historyPending))
 			t.historyIndex--
 		default:
 			entry, ok := t.history.NthPreviousEntry(t.historyIndex - 1)
 			if ok {
 				t.historyIndex--
-				t.setLine([]byte(entry), len(entry))
+				t.setLine([]rune(entry), len(entry))
 			}
 		}
 	case keyEnter:
 		t.moveCursorToPos(len(t.line))
-		t.queue([]byte("\r\n"))
+		t.queue([]rune("\r\n"))
 		line = string(t.line)
 		ok = true
 		t.line = t.line[:0]
@@ -441,12 +448,15 @@
 		t.moveCursorToPos(t.pos)
 	default:
 		if t.AutoCompleteCallback != nil {
+			prefix := string(t.line[:t.pos])
+			suffix := string(t.line[t.pos:])
+
 			t.lock.Unlock()
-			newLine, newPos := t.AutoCompleteCallback(t.line, t.pos, key)
+			newLine, newPos, completeOk := t.AutoCompleteCallback(prefix+suffix, len(prefix), key)
 			t.lock.Lock()
 
-			if newLine != nil {
-				t.setLine(newLine, newPos)
+			if completeOk {
+				t.setLine([]rune(newLine), utf8.RuneCount([]byte(newLine)[:newPos]))
 				return
 			}
 		}
@@ -457,13 +467,13 @@
 			return
 		}
 		if len(t.line) == cap(t.line) {
-			newLine := make([]byte, len(t.line), 2*(1+len(t.line)))
+			newLine := make([]rune, len(t.line), 2*(1+len(t.line)))
 			copy(newLine, t.line)
 			t.line = newLine
 		}
 		t.line = t.line[:len(t.line)+1]
 		copy(t.line[t.pos+1:], t.line[t.pos:])
-		t.line[t.pos] = byte(key)
+		t.line[t.pos] = key
 		if t.echo {
 			t.writeLine(t.line[t.pos:])
 		}
@@ -473,7 +483,7 @@
 	return
 }
 
-func (t *Terminal) writeLine(line []byte) {
+func (t *Terminal) writeLine(line []rune) {
 	for len(line) != 0 {
 		remainingOnLine := t.termWidth - t.cursorX
 		todo := len(line)
@@ -525,7 +535,7 @@
 		return
 	}
 
-	t.queue([]byte(t.prompt))
+	t.queue([]rune(t.prompt))
 	chars := len(t.prompt)
 	if t.echo {
 		t.queue(t.line)
@@ -572,7 +582,7 @@
 	// t.lock must be held at this point
 
 	if t.cursorX == 0 && t.cursorY == 0 {
-		t.writeLine([]byte(t.prompt))
+		t.writeLine([]rune(t.prompt))
 		t.c.Write(t.outBuf)
 		t.outBuf = t.outBuf[:0]
 	}
@@ -581,9 +591,9 @@
 		rest := t.remainder
 		lineOk := false
 		for !lineOk {
-			var key int
+			var key rune
 			key, rest = bytesToKey(rest)
-			if key < 0 {
+			if key == utf8.RuneError {
 				break
 			}
 			if key == keyCtrlD {
diff --git a/terminal_test.go b/terminal_test.go
index 75584d3..6ea92d9 100644
--- a/terminal_test.go
+++ b/terminal_test.go
@@ -137,6 +137,10 @@
 		in:   "ab\x1b[D\013\r",
 		line: "a",
 	},
+	{
+		in:   "Ξεσκεπάζω\r",
+		line: "Ξεσκεπάζω",
+	},
 }
 
 func TestKeyPresses(t *testing.T) {