parse error in create index

Hi,

could someone, please, explain me the following parse error?

adressen=> \d geburtstage
Table    = geburtstage
+----------------------------------+----------------------------------+-------+
|              Field               |              Type                |
Length|
+----------------------------------+----------------------------------+-------+
| lfd_nr                           | int4                            
|     4 |
| geburtstag                       | date                            
|     4 |
+----------------------------------+----------------------------------+-------+
adressen=> create index Monat_Tag on geburtstage (date_part('month',
Geburtstag));
ERROR:  parser: parse error at or near "'"
adressen=>

Thanks in advance,

-- 
Hubert Palme
palme@uni-wuppertal.de