Confusing compiler error when static missing in generic

[n5m]

Current Output

Compiling the following file fails and produces an unhelpful error.

# mvp.nim
type ArrayBlock[I, T] = object
  data*: array[I, T]

var s: ArrayBlock[30, int]

user@user:~$ nim c mvp.nim 
Hint: used config file '/home/user/nim/config/nim.cfg' [Conf]
Hint: used config file '/home/user/nim/config/config.nims' [Conf]
....fatal.nim(49)            sysFatal
Error: unhandled exception: int128.nim(72, 11) `arg.sdata(2) == 0` out of range [AssertionDefect]

Changing the type definition to

type ArrayBlock[I: static[Natural], T]

removes the compilation error, but the error message does not suggest that.

Additional Information

git hash: fa5f225

user@user:~$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2020-11-06
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: fa5f225efc7161110b0d4cf57e86646f2b0d97f8
active boot switches: -d:release