Japan is aiming to conclude its current trade negotiations with the U.K. by the end of next month, according to a Japanese government official familiar with the talks.

While the time frame sounds very short for a trade negotiation, the two sides aren’t starting from scratch because they already have an economic partnership agreement, the official said.

Hiroshi Matsuura, Tokyo’s chief negotiator in the talks, earlier told the Financial Times that his nation was giving the U.K. six weeks to strike a post-Brexit trade deal so both sides needed to limit their ambitions.

Japan wants to close the deal early as it will need time to check each detail before it can be sent to the Diet for approval, according to the government official. The Diet is expected to start an extra session this autumn.

Securing trade deals is a top priority for the U.K. as it emerges into a post-Brexit world. Without a new accord, the two countries will default to trading on World Trade Organization terms.

Japan is the U.K.’s fourth-largest non-EU trading partner. The U.K. was Japan’s 15th largest trading partner last year.