plpgsql error

I get this error when I try to create a function using plpgsql:

ERROR:  Unrecognized language specified in a CREATE FUNCTION: 'plpgsql'.
Recognized languages are sql, C, internal and the created procedural
languages.

Do I need to specify another flag when I compile Postgresql?

Adam
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Si hoc legere scis nimium eruditionis habes.