Before this patch:

  'a'[0] = 1        #=> 1
  'a'[:a] = '1'     #=> ArgumentError
  'a'[:a, 0] = '1'  #=> ArgumentError
  'a'[0, :a] = '1'  #=> ArgumentError
  'a'[0, 1] = 1     #=> 1

After this patch / Ruby:

  'a'[0] = 1        #=> TypeError
  'a'[:a] = '1'     #=> TypeError
  'a'[:a, 0] = '1'  #=> TypeError
  'a'[0, :a] = '1'  #=> TypeError
  'a'[0, 1] = 1     #=> TypeError