diff --git a/postgresql.postinstall b/postgresql.postinstall
index 610406f..45c2a61 100644
--- a/postgresql.postinstall
+++ b/postgresql.postinstall
@@ -17,7 +17,7 @@ chown postgres:postgres /opt/postgresql
 chown postgres:postgres /var/opt/postgresql/data/
 
 # create the initial cluster (WARNING!! this cluster will be SQL_ASCII)
-su -c "/opt/postgresql/bin/initdb -D /var/opt/postgresql/data" postgres
+su - postgres -c "/opt/postgresql/bin/initdb -D /var/opt/postgresql/data"
 
 # enable the X5 compatibility options
 sed -i -e "s,^#default_with_oids\ =\ off,default_with_oids\ =\ on," \