diff --git a/squinnondation/peers.py b/squinnondation/peers.py
index 0f69edd..e20701d 100644
--- a/squinnondation/peers.py
+++ b/squinnondation/peers.py
@@ -669,7 +669,7 @@ class User(Peer):
         Remove messages which are overdue (older than 2 minutes) from the inundation dictionnary.
         """
         self.data_lock.acquire()
-        for key in self.recent_messages:
+        for key in self.recent_messages.copy():
             if time.time() - self.recent_messages[key][1] > 120:
                 self.recent_messages.pop(key)
         self.data_lock.release()