Segmentation fault sprintf("%05b", -5)

[ksss]

mruby: ef30530

$ mruby -e 'sprintf("%0b", -5)'
#=> segmentation fault

build_config.rb

MRuby::Build.new('test') do |conf|
  toolchain :gcc
  enable_debug
  conf.gembox 'default'
end

lldb

frame #5: 0x00000001001aa208 mruby`mrb_str_format(mrb=0x000061400000a440, argc=2, argv=0x000061d00001d6a0, fmt=mrb_value @ 0x00007fff5fbf3120) at sprintf.c:987
   984
   985 	        if (v < 0) {
   986 	          char c = sign_bits(base, p);
-> 987 	          FILL(c, prec - len);
   988 	        }
   989 	        else if ((flags & (FMINUS|FPREC)) != FMINUS) {
   990 	          char c = '0';
(lldb) p prec
(mrb_int) $1 = -3
(lldb) p len
(mrb_int) $2 = 4

mruby/mrbgems/mruby-sprintf/src/sprintf.c

Line 987 in ef30530

FILL(c, prec - len);

[ksss]

before #3645

$ mruby -e 'sprintf("%05b", -5)'
illegal specifier (ArgumentError)

[ksss]

expect:

$ ruby -e 'p sprintf("%05b", -5)'
"..1011"