diff --git a/regress/cmd-parse-assignment.sh b/regress/cmd-parse-assignment.sh
new file mode 100644
index 000000000..53ec4b9f0
--- /dev/null
+++ b/regress/cmd-parse-assignment.sh
@@ -0,0 +1,69 @@
+#!/bin/sh
+
+# A bare assignment in a command sequence must not discard earlier commands.
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+CONF=$(mktemp)
+trap '$TMUX kill-server 2>/dev/null; rm -f "$CONF"' 0
+trap 'exit 1' 1 2 15
+$TMUX new-session -d || exit 1
+
+check()
+{
+	name=$1
+	expected=$2
+	$TMUX set -g @trace '' || exit 1
+	$TMUX set-environment -gu PARSE_ASSIGN || exit 1
+	printf '%s\n' "$3" >"$CONF"
+	$TMUX source-file "$CONF" || exit 1
+	trace=$($TMUX show-options -gqv @trace) || exit 1
+	assignment=$($TMUX show-environment -g PARSE_ASSIGN 2>/dev/null)
+	out="$trace:$assignment"
+	if [ "$out" != "$expected" ]; then
+		echo "$name: expected '$expected', got '$out'"
+		cat "$CONF"
+		exit 1
+	fi
+}
+
+check trailing 'ab:PARSE_ASSIGN=1' \
+    'set -ag @trace a; set -ag @trace b; PARSE_ASSIGN=1'
+check middle 'ab:PARSE_ASSIGN=1' \
+    'set -ag @trace a; PARSE_ASSIGN=1; set -ag @trace b'
+check leading 'ab:PARSE_ASSIGN=1' \
+    'PARSE_ASSIGN=1; set -ag @trace a; set -ag @trace b'
+check repeated 'ab:PARSE_ASSIGN=2' \
+    'set -ag @trace a; PARSE_ASSIGN=1; set -ag @trace b; PARSE_ASSIGN=2'
+check semicolon 'a:PARSE_ASSIGN=1' \
+    'set -ag @trace a; PARSE_ASSIGN=1;'
+check standalone ':PARSE_ASSIGN=1' 'PARSE_ASSIGN=1'
+check braces 'ab:PARSE_ASSIGN=1' \
+    'if-shell -F 1 { set -ag @trace a; set -ag @trace b; PARSE_ASSIGN=1 }'
+check active 'ab:PARSE_ASSIGN=1' \
+    '%if 1 set -ag @trace a; set -ag @trace b; PARSE_ASSIGN=1 %endif'
+check inactive ':' \
+    '%if 0 set -ag @trace a; set -ag @trace b; PARSE_ASSIGN=1 %endif'
+
+# An assignment must not hide an invalid command earlier in the sequence.
+$TMUX set -g @trace '' || exit 1
+printf '%s\n' \
+    'set -ag @trace a; nonexistent-command; PARSE_ASSIGN=1' >"$CONF"
+if out=$($TMUX source-file "$CONF" 2>&1); then
+	echo 'Invalid command before assignment was ignored'
+	exit 1
+fi
+if [ "$out" != "$CONF:1: unknown command: nonexistent-command" ]; then
+	echo "Unexpected parse error: '$out'"
+	exit 1
+fi
+trace=$($TMUX show-options -gqv @trace) || exit 1
+if [ -n "$trace" ]; then
+	echo 'Commands executed despite a parse error'
+	exit 1
+fi
+
+exit 0