Integer constant expression expected instead of...

[Era Scarecrow]

[code]
  enum fieldEntryLength = 4;
  //immutable fieldEntryLength = 4; //same issue
  alias immutable(char[fieldEntryLength]) NString;
[/code]
test.d(10): Error: Integer constant expression expected instead 
of fieldEntryLength


 This breaks code that previously compiled. I really don't see 
the problem... bug?

 Version: Windows DMD32 D Compiler v2.063.2