Sybase SQL CASE statement problem

Hello Experts, I am creating a SQL query in Crystal Reports to run against a Sybase db. My select statement is
SELECT
ad.line1
  case
    when en.firm is not NULL then en.firm
     else en.first_name || ' ' || en.last_name AS Name
 end
  case
    when en.taxid is not NULL then en.taxid
     else en.ssno
 end
 FROM  
The CASE statements are not working. What am I doing wrong? Should I use COALESCE instead? If so, how would I write that?