diff --git a/CHANGES b/CHANGES
index eaf7576da..5c4ff9664 100644
--- a/CHANGES
+++ b/CHANGES
@@ -87,6 +87,9 @@ CHANGES FROM 3.7b TO 3.8
   while scrolling or while hovered and disappears after pane-scrollbars-timeout
   (Michael Grant).
 
+* Add a #{A/count:frames} modifier to show a series of frames as an animation
+  in the status line (issue 5412 from Fernando Daciuk).
+
 * Change command templates so %% is escaped for single quotes while %1 remains
   unquoted, preventing single quotes in session or target names from
   terminating quoted command sections (reported by Aliz Hammond).
diff --git a/regress/format-animation.sh b/regress/format-animation.sh
new file mode 100644
index 000000000..b62b04444
--- /dev/null
+++ b/regress/format-animation.sh
@@ -0,0 +1,109 @@
+#!/bin/sh
+
+# Exercise the A format modifier (format_cycle in format.c). It is expanded
+# only in a status format and arms the client cycle timer to redraw the status
+# line as the frames advance, so the only place its behaviour shows is a
+# rendered status line.
+#
+# The status line is rendered by an inner tmux attached inside an outer tmux
+# pane; capturing the outer pane shows what the inner tmux drew. The inner
+# window runs sleep and every other status line is blanked, so the capture
+# contains the frame and nothing else.
+#
+# Each frame lasts 700 milliseconds and the capture is repeated once a second,
+# so consecutive samples always land on a different frame: no exact period is
+# assumed and nothing in the test asks for a redraw, so seeing the frame change
+# means the status line animated on its own.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+TMP=$(mktemp)
+trap "rm -f $TMP; $TMUX kill-server 2>/dev/null; $TMUX2 kill-server 2>/dev/null" \
+	0 1 15
+
+fail() {
+	echo "$*" >&2
+	exit 1
+}
+
+# Capture the outer pane and return the text the inner tmux drew.
+capture() {
+	$TMUX capturep -p >$TMP || fail "capture failed"
+	tr -d '[:space:]' <$TMP
+}
+
+$TMUX kill-server 2>/dev/null
+$TMUX2 kill-server 2>/dev/null
+
+# Inner: a window which draws nothing and a status line which is only the
+# animation, so the outer capture is the current frame on its own.
+$TMUX2 new -d -x30 -y8 "sh -c 'exec sleep 100'" || exit 1
+$TMUX2 set -g window-size latest || exit 1
+i=1
+while [ $i -le 4 ]; do
+	$TMUX2 set -g status-format[$i] "" || exit 1
+	i=$((i + 1))
+done
+$TMUX2 set -g status-format[0] "#{A/7:AAAA,BBBB,CCCC}" || exit 1
+
+$TMUX new -d -x30 -y8 || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g window-size manual || exit 1
+$TMUX set -g default-terminal "tmux-256color" || exit 1
+$TMUX send -l "$TMUX2 attach" || exit 1
+$TMUX send Enter || exit 1
+sleep 1
+
+# Sample the frames. Every sample must be one of the frames and at least two
+# different ones must be seen; status-interval is 15 seconds so only the cycle
+# timer can have redrawn the status line.
+seen=""
+i=0
+while [ $i -lt 4 ]; do
+	[ $i -eq 0 ] || sleep 1
+	frame=$(capture)
+	case "$frame" in
+	AAAA|BBBB|CCCC) ;;
+	*) fail "status line is '$frame', not a frame" ;;
+	esac
+	case " $seen " in
+	*" $frame "*) ;;
+	*) seen="$seen $frame" ;;
+	esac
+	i=$((i + 1))
+done
+set -- $seen
+[ $# -ge 2 ] || fail "status line did not animate, only saw$seen"
+
+# Outside a status format there is no animation at all.
+out=$($TMUX2 display-message -p "#{A:ZZZZ,YYYY}") || exit 1
+[ -z "$out" ] || fail "display-message gave '$out', want empty"
+out=$($TMUX2 list-panes -F "#{A:ZZZZ,YYYY}") || exit 1
+[ -z "$out" ] || fail "list-panes gave '$out', want empty"
+
+# Nor inside #(), where the frames would change the command on every frame.
+$TMUX2 set -g status-format[0] '#(echo "[#{A:ZZZZ,YYYY}]")' || exit 1
+sleep 1
+out=$(capture)
+case "$out" in
+*ZZZZ*|*YYYY*) fail "job command saw a frame: '$out'" ;;
+*"[]"*) ;;
+*) fail "job output is '$out', want []" ;;
+esac
+
+# Empty frames and a missing or bad count must not upset the server.
+for f in '#{A:}' '#{A/0:a,b}' '#{A/x:a,b}' '#{A:,,,}'; do
+	$TMUX2 set -g status-format[0] "$f" || fail "setting $f failed"
+	$TMUX2 has-session >/dev/null 2>&1 || fail "server lost with $f"
+done
+sleep 1
+$TMUX2 has-session >/dev/null 2>&1 || fail "server lost after empty frames"
+
+exit 0