I am trying to perform a COUNTROWS on a filtered table where column 'galaxies'[name] = "Milky Way"

Here is my dax measure:

test_measure = 
  COUNTROWS(
    FILTER(
      'galaxies',
      'galaxies'[name] = "Milky Way"
      )
  )

When I run this, I receive an error saying "The expression specified in the query is not a valid table expression".

Why is this an error? FILTER returns a table and COUNTROWS takes a table as its argument.