[Monetdb-developers] About data type "interval"

Dear Sir/Madam: I came across a problem when running a SQL statement: select l_linestatus from lineitem where shipdate <= date '1998-12-01' - interval '1 day' //I want to search the records whose shipdate is prior to the day before Dec. 1998

But MonetDB returned me with the error message: syntax error, unexpected SCOLON in: "select ...," the whole SQL sentence above, What's wrong? Thank you!

eric