With the attached files the problem can be reproduced predictability: Save the attached files b.h.master and b.h.next to a directory and cd to it. $ emacs -Q & $ cp b.h.master b.h C-x C-f b.h $ cp b.h.next b.h M-x revert-buffer and the args-out-of-range error pops: c-clear-char-property-with-value-function: Args out of range: 166, 453 I was unable to try with the latest Emacs sources because the build is broken. My Emacs is from the 16 September.