highlight --force on bare text crashes or outputs garbage

Doing this on current arch package of highlight (3.51-1) causes a segmentation fault:

echo Hi | highlight --force --fragment

If you remove the --fragment the segmentation fault happens after the HTML header, but still happens.

I tried to reproduce this by building from git, on that i get unpredictable behaviour of either outputting some garbage (which sometimes changes in repeated runs) followed by a newline or a segmentation fault:

[urjaman@apuarch src]$ cat text
Hi
[urjaman@apuarch src]$ ./highlight  --fragment --force -O html  < text | hexdump -C
00000000  49 89 c3 b8 ee 0a                                 |I.....|
00000006
<repeat the same 3 times, and then...>
[urjaman@apuarch src]$ ./highlight  --fragment --force -O html  < text | hexdump -C
00000000  e4 46 0a                                          |.F.|
00000003