Left join ON not null columns can't select not null column

Each table has a column RECNUM. They are (decimal(28,0), not null). That is where I am doing my join. I want to select the column DESC in CAUNIT. It is (varchar(28,0), not null). When I run my query I get:

Msg 156, Level 15, State 1, Line 1 Incorrect syntax near the keyword 'DESC'. Below is my query:

SELECT CDCLSVC.UNIT_ID,CAUNIT.DESC
FROM CDCLSVC
LEFT JOIN CAUNIT
ON CDCLSVC.RECNUM = CAUNIT.RECNUM