Dedent fails in block

This is not a practical example, but a dedent inside a block (using map here) fails:

>> [1,2,3].map do |i|
..    [2,3,4].map do |n|
..      i ** n      
..
=> [[1,1,1],[4,8,16],[9,27,81]]
>> [1,2,3].map do |i|
..    [2,3,4].map do |n|
..      i ** n      
..    i * 3
..
Error: Line 4: syntax error before: i