Judge Robert Patterson of the Manhattan District Court said in an opinion that US publisher RDR Books would violate copyright by publishing Steve Vander Ark's "Harry Potter Lexicon."

The ruling said that RDR Books "failed to establish an affirmative defense of fair use," the court clerk told AFP.

The lawsuit was brought by Rowling and Warner Brothers Entertainment.

Patterson awarded damages of 6,750 dollars to Warner and to Rowling, said by Forbes magazine to be the richest author on the planet thanks to the magical success of her bespectacled hero.

Rowling declared herself "delighted," but insisted in a statement that she took "no pleasure at all" in seeing off her over-ambitious fan.

In a court hearing this April, Rowling almost broken down as she described her shock at seeing Harry Potter and his fellow sorcerers appear in someone else's book.

"It was all my life, apart from my children," she said.

Vander Ark was motivated only by his love of the series, which he had read many times over, according to his lawyer.

But Rowling said that she had planned her own reference guide to the stories, which have sold almost 350 million copies around the world in some 65 languages and spawned a series of films.

She said in her statement Monday that "the proposed book took an enormous amount of my work and added virtually no original commentary of its own.

"Many books have been published which offer original insights into the world of Harry Potter. The Lexicon just is not one of them."

Michigan-based RDR Books, which described the case on its website as a "David and Goliath" struggle, could not be immediately reached for comment.