kernel : sending pkt_too_big (len[1500] pmtu[1486]) to self

I'm getting errors like this:

Oct 27 05:02:54 hostname kernel: sending pkttoobig (len[1500] pmtu[1486]) to self

Oct 27 05:04:54 hostname kernel: sending pkttoobig (len[1500] pmtu[1486]) to self

in my logs…. sometimes in ones or twos, sometimes in batches of about 10 or more. I can't figure out why this is happening, it doesn't seem to correspond with any abnormal other event, and all the things I find about this error on google are either dated over 2 years ago, unreplied to, or in bulgarian. :-(

Any suggestions as to what is causing this to suddenly appear during normal operation would be most appreciated. (I suspect it might be some file transfer program setting its packet size too large, but that's just a guess).