PostgreSQL trap, and assertion failed

Hello,

I have small crash reporting code, which I use during mmap-ing database. After
last merge with master I got

TRAP: FailedAssertion("!(slot > 0 && slot <= PMSignalState->num_child_flags)",
File: "pmsignal.c", Line: 227)
LOG:  server process (PID 5128) was terminated by signal 6: Aborted
LOG:  terminating any other active server processes
TRAP: FailedAssertion("!(slot > 0 && slot <= PMSignalState->num_child_flags)",
File: "pmsignal.c", Line: 189)

I've installed crash reports on sigbus and sigseg signals. May I ask what may
be wrong, and how to prevent this?

Regards,
Radek.