diff --git a/regress/copy-mode-unicode-whitespace.sh b/regress/copy-mode-unicode-whitespace.sh
new file mode 100755
index 000000000..a532606a8
--- /dev/null
+++ b/regress/copy-mode-unicode-whitespace.sh
@@ -0,0 +1,163 @@
+#!/bin/sh
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+fail()
+{
+	echo "$1"
+	[ -z "$TMUX" ] || $TMUX kill-server 2>/dev/null
+	exit 1
+}
+
+goto_cell()
+{
+	row=$1
+	column=$2
+
+	$TMUX send-keys -X history-top || fail "$mode: history-top failed"
+	$TMUX send-keys -X start-of-line || fail "$mode: start-of-line failed"
+	[ "$row" -eq 0 ] ||
+	    $TMUX send-keys -X -N "$row" cursor-down ||
+	    fail "$mode: cursor-down failed"
+	[ "$column" -eq 0 ] ||
+	    $TMUX send-keys -X -N "$column" cursor-right ||
+	    fail "$mode: cursor-right failed"
+}
+
+check_cursor()
+{
+	expected=$1
+	actual=$($TMUX display-message -p '#{copy_cursor_x},#{copy_cursor_y}')
+	[ "$actual" = "$expected" ] ||
+	    fail "$mode: expected cursor $expected, got $actual"
+}
+
+check_word()
+{
+	row=$1
+	column=$2
+	expected=$3
+
+	goto_cell "$row" "$column"
+	$TMUX set-buffer sentinel || fail "$mode: set-buffer failed"
+	$TMUX send-keys -X select-word || fail "$mode: select-word failed"
+	$TMUX send-keys -X copy-selection || fail "$mode: copy-selection failed"
+	actual=$($TMUX show-buffer 2>/dev/null)
+	[ "$actual" = "$expected" ] ||
+	    fail "$mode: expected word '$expected', got '$actual'"
+}
+
+check_next_word()
+{
+	row=$1
+	expected=$2
+
+	goto_cell "$row" 0
+	$TMUX send-keys -X next-word || fail "$mode: next-word failed"
+	$TMUX set-buffer sentinel || fail "$mode: set-buffer failed"
+	$TMUX send-keys -X select-word || fail "$mode: select-word failed"
+	$TMUX send-keys -X copy-selection || fail "$mode: copy-selection failed"
+	actual=$($TMUX show-buffer 2>/dev/null)
+	[ "$actual" = "$expected" ] ||
+	    fail "$mode: expected next word '$expected', got '$actual'"
+}
+
+for mode in emacs vi; do
+	TMUX="$TEST_TMUX -Lunicode-whitespace-$mode-$$ -f/dev/null"
+	$TMUX kill-server 2>/dev/null
+	$TMUX new-session -d -x16 -y20 \
+	    "printf 'aa bb\naa\tbb\naa\302\240bb\naa\343\200\200bb\naa:bb\naaaaaaaaaaaaaaa\302\240b\nabcdefghijklmnopq\nhardone\nhardtwo\naa\341\232\200bb\naa\342\200\200bb\naa\342\200\250bb\naa\342\200\251bb\naa\342\200\257bb\naa\342\201\237bb\nxa\302\205b c\n'; exec cat" ||
+	    fail "$mode: new-session failed"
+	$TMUX set-option -g window-size manual || fail "$mode: set size failed"
+	$TMUX set-window-option -g mode-keys "$mode" ||
+	    fail "$mode: set mode-keys failed"
+	$TMUX set-window-option -g word-separators "" ||
+	    fail "$mode: clear word-separators failed"
+	$TMUX copy-mode || fail "$mode: copy-mode failed"
+
+	# ASCII space and TAB retain their existing behaviour.
+	goto_cell 0 0
+	$TMUX send-keys -X next-space || fail "$mode: ASCII next-space failed"
+	check_cursor 3,0
+	goto_cell 1 0
+	$TMUX send-keys -X next-space || fail "$mode: TAB next-space failed"
+	check_cursor 8,1
+	$TMUX send-keys -X previous-space ||
+	    fail "$mode: TAB previous-space failed"
+	check_cursor 0,1
+
+	# NBSP is whitespace for selection and word movement.
+	goto_cell 2 0
+	$TMUX send-keys -X next-word || fail "$mode: NBSP next-word failed"
+	check_cursor 3,2
+	$TMUX send-keys -X previous-word ||
+	    fail "$mode: NBSP previous-word failed"
+	check_cursor 0,2
+	check_word 2 0 aa
+	goto_cell 2 0
+	$TMUX send-keys -X next-word-end ||
+	    fail "$mode: NBSP next-word-end failed"
+	if [ "$mode" = emacs ]; then
+		check_cursor 2,2
+	else
+		check_cursor 1,2
+	fi
+
+	# U+3000 is two columns wide; both its leading and padding cells must be
+	# skipped as one whitespace character in either direction.
+	goto_cell 3 0
+	$TMUX send-keys -X next-word || fail "$mode: U+3000 next-word failed"
+	check_cursor 4,3
+	$TMUX send-keys -X previous-word ||
+	    fail "$mode: U+3000 previous-word failed"
+	check_cursor 0,3
+	goto_cell 3 0
+	$TMUX send-keys -X next-space-end ||
+	    fail "$mode: U+3000 next-space-end failed"
+	if [ "$mode" = emacs ]; then
+		check_cursor 2,3
+	else
+		check_cursor 1,3
+	fi
+
+	# Other characters in word-separators remain literal when space enables
+	# Unicode whitespace matching.
+	$TMUX set-window-option -g word-separators ': ' ||
+	    fail "$mode: set custom word-separators failed"
+	goto_cell 4 0
+	$TMUX send-keys -X next-word || fail "$mode: literal next-word failed"
+	check_cursor 2,4
+	$TMUX set-window-option -g word-separators "" ||
+	    fail "$mode: restore word-separators failed"
+
+	# Whitespace in the last column remains a boundary across a soft wrap.
+	goto_cell 5 0
+	$TMUX send-keys -X next-space ||
+	    fail "$mode: wrapped NBSP next-space failed"
+	check_cursor 0,6
+
+	# A word split only by a soft wrap remains one word, while a hard line
+	# boundary still terminates selection.
+	check_word 7 0 abcdefghijklmnopq
+	check_word 9 0 hardone
+
+	# Check the remaining representative White_Space ranges and U+0085
+	# combined into a cell with another character.
+	check_next_word 11 bb
+	check_next_word 12 bb
+	check_next_word 13 bb
+	check_next_word 14 bb
+	check_next_word 15 bb
+	check_next_word 16 bb
+	goto_cell 17 0
+	$TMUX send-keys -X next-word ||
+	    fail "$mode: combined U+0085 next-word failed"
+	check_cursor 2,17
+
+	$TMUX kill-server 2>/dev/null
+done
+
+exit 0