In line 869: offset = i + 1 - strlen (match);

offset can become -1, which leads to an illegale memory write to
matchrepl[-1] further down.
The problem appears when I use a Turkish dictionary, and the error may
caused by bad data in
the dictionary hyph_tr.dic from
https://github.com/Slyneth/hunspell-hyphenation-turkish

hyphen.c

@@ -882,6 +882,7 @@ int hnj_hyphen_hyph_(HyphenDict *dict, const char *word, int word_size,
       if (match)
 	{
 	  offset = i + 1 - strlen (match);
+	  if (offset < 0) offsent = 0;	// happens with hyph_tr.dic
 #ifdef VERBOSE
 	  for (k = 0; k < offset; k++)
 	    putchar (' ');