diff --git a/modules/seen.py b/modules/seen.py
index 729764a..1467c45 100755
--- a/modules/seen.py
+++ b/modules/seen.py
@@ -140,6 +140,7 @@ def dump_seen_db(bot):
 @hook(True)
 @require_chanmsg
 def seen_hook(bot, trigger):
+	bot.memory["seen_lock"].acquire()
 	last = (time.time(), trigger.channel, trigger.group(0))
 	if not trigger.nick in bot.memory["seen"]:
 		first = (time.time(), trigger.channel, trigger.group(0))
@@ -147,6 +148,7 @@ def seen_hook(bot, trigger):
 		first = bot.memory["seen"][trigger.nick][:3]
 	seen = first + last
 	bot.memory["seen"][trigger.nick] = seen
+	bot.memory["seen_lock"].release()
 
 	if time.time() - bot.memory["seen_last_dump"] > 1:
 		# only dump once a minute at most