The Nestlé company has been told it must prove that consumers can tell what a Kit Kat bar is if there are no markings or labels.
The European Court of Justice found against Nestlé which had wanted to trademark the shape of its chocolate bar in Britain.
Now the case is on its way back to the British High Court for a final ruling.
The Swiss food giant first filed a trademark application in 2010 but rival Cadbury appealed the following year. The court then rejected the application in 2013.
"It is up to the British courts to decide, on the basis of this response, if the form of Kit Kat chocolate bars can be registered as a trademark or not," the EU court said in a statement.
Nestlé holds that the Kit Kat shape is distinctive. But the ECJ judges ruled that the company had to prove that people perceive the shape “as originating from a particular company.”
"The trade mark applicant must prove that the relevant class of persons perceive the goods or services designated exclusively by the mark applied for, as opposed to any other mark which might also be present, as originating from a particular company," it said in its ruling.
Kit Kat bars were first sold in 1935. It was created by Rowntree but is now in the hands of Nestlé which acquired Rowntree in 1988. Kit Kats are marketed in large swathes of the globe, including most of the Americas, much of the Middle East and Asia, and Europe.
