Deputy Justice Minister Fred Teeven said that he might ignore the ruling.
"I have to consider it again and go look at the immediate circumstances," he said.
Fortuyn's brother Marten said in a statement on behalf of the family that "we presume Teeven will keep his word and see whether any provisional release can be prevented."
Geert Wilders, the politician who eventually won over the bulk of Fortuyn's former supporters and who currently tops national popularity polls, well ahead of Prime Minister Mark Rutte said that the criminal justice organization is "out of touch with reality."
"The interest of the Netherlands is that (Van der Graaf) remain behind bars as long as possible," he said.
At trial, Van der Graaf claimed he saw Fortuyn as a threat to the vulnerable, and compared Fortuyn's rise in popularity to the rise of Hitler. Closely questioned by judges, Van der Graaf said he wasn't sure whether what he did was wrong, but he said he would never do it again.
Van der Graaf was married and had a young daughter at the time of Fortuyn's killing.