diff --git a/regress/modal-pane.sh b/regress/modal-pane.sh
new file mode 100644
index 000000000..cd891281d
--- /dev/null
+++ b/regress/modal-pane.sh
@@ -0,0 +1,308 @@
+#!/bin/sh
+
+# Tests for modal floating panes.
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX kill-server >/dev/null 2>&1
+	$TMUX2 kill-server >/dev/null 2>&1
+}
+
+fail()
+{
+	echo "$*" >&2
+	cleanup
+	exit 1
+}
+
+must_equal()
+{
+	got=$1
+	want=$2
+	[ "$got" = "$want" ] || fail "got '$got', expected '$want'"
+}
+
+check_ok()
+{
+	$TMUX "$@" || fail "command failed: $*"
+}
+
+check_fail()
+{
+	exp="$1"
+	shift
+	out=$($TMUX "$@" 2>&1)
+	if [ $? -eq 0 ]; then
+		fail "command succeeded (expected failure): $*"
+	fi
+	must_equal "$out" "$exp"
+}
+
+fmt()
+{
+	$TMUX display-message -p -t "$1" "$2"
+}
+
+click()
+{
+	col="$1"
+	row="$2"
+	seq=$(printf '\033[<0;%s;%sM\033[<0;%s;%sm' \
+	    "$col" "$row" "$col" "$row")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 1
+}
+
+move_mouse()
+{
+	col="$1"
+	row="$2"
+	seq=$(printf '\033[<35;%s;%sM' "$col" "$row")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 1
+}
+
+ctrl_drag()
+{
+	scol="$1"
+	srow="$2"
+	ecol="$3"
+	erow="$4"
+
+	seq=$(printf '\033[<16;%s;%sM' "$scol" "$srow")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 0.2
+	seq=$(printf '\033[<48;%s;%sM' "$ecol" "$erow")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 0.2
+	seq=$(printf '\033[<16;%s;%sm' "$ecol" "$erow")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 1
+}
+
+drag()
+{
+	scol="$1"
+	srow="$2"
+	ecol="$3"
+	erow="$4"
+
+	seq=$(printf '\033[<0;%s;%sM' "$scol" "$srow")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 0.2
+	seq=$(printf '\033[<32;%s;%sM' "$ecol" "$erow")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 0.2
+	seq=$(printf '\033[<0;%s;%sm' "$ecol" "$erow")
+	$TMUX2 send-keys -t "$OUTER" -l "$seq" 2>/dev/null
+	sleep 1
+}
+
+cleanup
+
+check_ok new-session -d -s modal -x 80 -y 24 'cat'
+sleep 1
+p0=$(fmt modal:0 '#{pane_id}')
+check_ok split-window -h -t "$p0" 'cat'
+sleep 1
+p1=$(fmt modal:0 '#{pane_id}')
+
+check_ok select-pane -t "$p0"
+check_ok resize-pane -Z -t "$p0"
+must_equal "$(fmt modal:0 '#{window_zoomed_flag}')" 1
+
+modal=$($TMUX new-pane -OPF '#{pane_id}' -t "$p1" \
+    -x 20 -y 5 -X 20 -Y 10 'cat') ||
+	fail "new-pane -O failed"
+sleep 1
+must_equal "$(fmt "$modal" '#{pane_floating_flag}:#{pane_modal_flag}:#{pane_active}')" 1:1:1
+case "$(fmt "$modal" '#{pane_flags}')" in
+*O*) ;;
+*) fail "modal pane flags do not include O" ;;
+esac
+case "$(fmt modal:0 '#{window_flags}')" in
+*O*) ;;
+*) fail "modal window flags do not include O" ;;
+esac
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" "$modal"
+must_equal "$(fmt modal:0 '#{window_zoomed_flag}')" 0
+
+check_fail "window already has a modal pane" \
+	new-pane -O -x 10 -y 4 'cat'
+check_fail "modal pane must be floating" \
+	new-pane -O -L 'cat'
+check_fail "pane is modal" \
+	break-pane -s "$modal"
+check_fail "pane is modal" \
+	join-pane -s "$modal" -t "$p0"
+check_fail "pane is modal" \
+	join-pane -s "$p0" -t "$modal"
+check_fail "pane is modal" \
+	swap-pane -s "$modal" -t "$p0"
+check_fail "pane is modal" \
+	swap-pane -s "$p0" -t "$modal"
+
+check_ok select-pane -t "$p1"
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+check_ok last-pane -t modal:0
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+
+under=$($TMUX split-window -PF '#{pane_id}' -t "$p0" 'cat') ||
+	fail "split-window under modal failed"
+sleep 1
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+must_equal "$(fmt "$under" '#{pane_active}')" 0
+
+float=$($TMUX new-pane -PF '#{pane_id}' -x 10 -y 4 -X 5 -Y 3 'cat') ||
+	fail "new floating pane under modal failed"
+sleep 1
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+must_equal "$(fmt "$float" '#{pane_active}')" 0
+
+check_ok new-window -d -t modal: -n other 'cat'
+check_ok select-window -t modal:other
+other=$(fmt modal:other '#{pane_id}')
+must_equal "$(fmt modal:other '#{pane_id}')" "$other"
+check_ok select-window -t modal:0
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+
+check_ok send-keys -t modal:0 'modal-key' Enter
+sleep 1
+case "$($TMUX capture-pane -pt "$modal")" in
+*modal-key*) ;;
+*) fail "keyboard input did not reach modal pane" ;;
+esac
+case "$($TMUX capture-pane -pt "$p0")" in
+*modal-key*) fail "keyboard input reached pane below modal" ;;
+esac
+
+$TMUX set -g mouse on
+$TMUX set -g focus-follows-mouse on
+$TMUX set -g @modal-mouse ''
+$TMUX bind -n MouseDown1Pane run-shell \
+    "$TMUX set -g @modal-mouse '#{mouse_pane}'"
+$TMUX bind x set -g @modal-prefix yes
+
+$TMUX2 new-session -d -x 80 -y 24 "$TMUX attach -t modal" ||
+	fail "outer session failed"
+sleep 1
+OUTER=$($TMUX2 list-panes -F '#{pane_id}' | head -1)
+[ -n "$OUTER" ] || fail "no outer pane"
+
+click 1 1
+must_equal "$($TMUX show -gv @modal-mouse)" ''
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+
+panes=$(fmt modal:0 '#{window_panes}')
+ctrl_drag 1 1 8 3
+must_equal "$(fmt modal:0 '#{window_panes}')" "$panes"
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+
+move_mouse 1 1
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+
+left=$(fmt "$modal" '#{pane_left}')
+top=$(fmt "$modal" '#{pane_top}')
+click $((left + 1)) $((top + 1))
+must_equal "$($TMUX show -gv @modal-mouse)" "$modal"
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+
+width=$(fmt "$modal" '#{pane_width}')
+right=$((left + width + 1))
+drag "$right" $((top + 1)) $((right + 5)) $((top + 1))
+new_width=$(fmt "$modal" '#{pane_width}')
+[ "$new_width" -gt "$width" ] ||
+	fail "modal pane did not grow after right-border drag"
+
+$TMUX2 send-keys -t "$OUTER" C-b x
+sleep 1
+must_equal "$($TMUX show -gv @modal-prefix)" yes
+
+$TMUX set-buffer -b modal-edit-test 'test'
+check_ok choose-buffer -t "$modal"
+panes=$(fmt modal:0 '#{window_panes}')
+$TMUX2 send-keys -t "$OUTER" e
+sleep 1
+must_equal "$(fmt modal:0 '#{window_panes}')" "$panes"
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" "$modal"
+$TMUX2 send-keys -t "$OUTER" q
+sleep 1
+
+check_ok kill-pane -t "$modal"
+sleep 1
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" ''
+case "$(fmt modal:0 '#{window_flags}')" in
+*O*) fail "modal window flag remained after modal pane closed" ;;
+esac
+must_equal "$(fmt modal:0 '#{pane_id}')" "$p0"
+must_equal "$(fmt modal:0 '#{window_zoomed_flag}')" 1
+check_ok resize-pane -Z -t "$p0"
+must_equal "$(fmt modal:0 '#{window_zoomed_flag}')" 0
+
+$TMUX set -g editor 'sh -c "sleep 10" sh'
+check_ok resize-pane -Z -t "$p0"
+check_ok choose-buffer -t "$p0"
+panes=$(fmt modal:0 '#{window_panes}')
+$TMUX2 send-keys -t "$OUTER" e
+sleep 1
+editor=$(fmt modal:0 '#{window_modal_pane}')
+[ -n "$editor" ] || fail "buffer editor did not open as modal pane"
+must_equal "$(fmt modal:0 '#{window_panes}')" $((panes + 1))
+must_equal "$(fmt "$editor" '#{pane_modal_flag}:#{pane_active}')" 1:1
+check_ok kill-pane -t "$editor"
+sleep 1
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" ''
+must_equal "$(fmt modal:0 '#{pane_id}')" "$p0"
+must_equal "$(fmt modal:0 '#{window_zoomed_flag}')" 1
+check_ok resize-pane -Z -t "$p0"
+must_equal "$(fmt modal:0 '#{window_zoomed_flag}')" 0
+
+detached=$($TMUX new-pane -OdPF '#{pane_id}' -x 20 -y 5 -X 20 -Y 10 \
+    'cat') || fail "new detached modal failed"
+sleep 1
+must_equal "$(fmt "$detached" '#{pane_modal_flag}:#{pane_active}')" 1:1
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" "$detached"
+check_ok kill-pane -t "$detached"
+sleep 1
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" ''
+must_equal "$(fmt modal:0 '#{pane_id}')" "$p0"
+
+$TMUX set -g @modal-custom old
+check_ok customize-mode -t "$p0" \
+	-f '#{==:#{option_name},@modal-custom}'
+panes=$(fmt modal:0 '#{window_panes}')
+$TMUX2 send-keys -t "$OUTER" j Right j e
+sleep 1
+editor=$(fmt modal:0 '#{window_modal_pane}')
+[ -n "$editor" ] || fail "customize editor did not open as modal pane"
+must_equal "$(fmt modal:0 '#{window_panes}')" $((panes + 1))
+must_equal "$(fmt "$editor" '#{pane_modal_flag}:#{pane_active}')" 1:1
+check_ok kill-pane -t "$editor"
+sleep 1
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" ''
+$TMUX2 send-keys -t "$OUTER" q
+sleep 1
+
+modal=$($TMUX new-pane -OkPF '#{pane_id}' -x 20 -y 5 -X 20 -Y 10 'printf done') ||
+	fail "new retained modal failed"
+sleep 2
+must_equal "$(fmt "$modal" '#{pane_dead}:#{pane_modal_flag}:#{pane_active}')" 1:1:1
+check_ok respawn-pane -k -t "$modal" 'cat'
+sleep 1
+must_equal "$(fmt "$modal" '#{pane_dead}:#{pane_modal_flag}:#{pane_active}')" 0:1:1
+check_ok select-pane -t "$p1"
+must_equal "$(fmt modal:0 '#{pane_id}')" "$modal"
+check_ok kill-pane -t "$modal"
+sleep 1
+must_equal "$(fmt modal:0 '#{window_modal_pane}')" ''
+must_equal "$(fmt modal:0 '#{pane_id}')" "$p0"
+
+cleanup
+exit 0