diff --git a/src/commands.py b/src/commands.py
index 9865457b9..e4685447e 100644
--- a/src/commands.py
+++ b/src/commands.py
@@ -120,6 +120,9 @@ def urlSnarfer(f):
         def doSnarf():
             _snarfLock.acquire()
             try:
+                # This has to be *after* we've acquired the lock so we can be
+                # sure that all previous urlSnarfers have already run to
+                # completion.
                 if msg.repliedTo:
                     self.log.debug('Not snarfing, msg is already repliedTo.')
                     return