It happened again. Both times I had pressed "G" which calls offlineimap and which removed messages that the notmuch database still thought are there. ---------------------------------------------------------------- Program received signal SIGSEGV, Segmentation fault. 0x00007ffff602bb14 in strncasecmp () from /lib/libc.so.6 (gdb) bt #0 0x00007ffff602bb14 in strncasecmp () from /lib/libc.so.6 #1 0x0000000000418521 in _thread_add_matched_message(_notmuch_thread*, _notmuch_message*, notmuch_sort_t) () #2 0x0000000000418b17 in _notmuch_thread_create () #3 0x000000000040e33c in notmuch_show_command () #4 0x0000000000408436 in main () ------------------------------------------------------------- spaetz@spaetz-macbook:~/src/notmuch$ notmuch show tag:inbox Error opening /home/spaetz/mail/INBOX.Junk/new/1272025029_0.17175.spaetz-macbook,U=3608,FMD5=22888fa7f8daa670f25d806e9b4ae4df:2,: No such file or directory Error opening /home/spaetz/mail/INBOX.Junk/new/1272025029_0.17175.spaetz-macbook,U=3608,FMD5=22888fa7f8daa670f25d806e9b4ae4df:2,: No such file or directory Error opening /home/spaetz/mail/INBOX.Junk/new/1272025029_0.17175.spaetz-macbook,U=3608,FMD5=22888fa7f8daa670f25d806e9b4ae4df:2,: No such file or directory Segmentation fault (core dumped) ---------------------------------------------------------- Coredump is here: http://sspaeth.de/uploads/tmp/core.bin ------------------------------------------------------------- Can it be that in thread.cc in _thread_add_matched_message () ... subject = notmuch_message_get_header (message, "subject"); if ((strncasecmp (subject, "Re: ", 4) == 0) || ... If the underlying message disappeared, get_header will return NULL and we pass strncasecmp NULL as first parameter. Could that be?