“Ghosts are real, that much I know,” is the first line spoken in Guillermo del Toro’s swooning Gothic thriller Crimson Peak, which opened to solid reviews but a tepid box office last weekend. In today’s global film economy, sub-par earnings in America don’t necessarily doom a film: Del Toro’s last effort, Pacific Rim, made up for its mediocre domestic performance by being a big hit overseas, especially in China. Producers are hoping the same will happen for Crimson Peak, but there’s one big problem. China’s Film Bureau doesn’t allow movies with ghosts in them, and certainly not movies that assert they’re “real.”

The intricacies of getting a film approved by the China Film Bureau, an executive branch of the country’s Communist government, are largely unknown to Western audiences. Sometimes it can take months or years to secure a release; many major films have run afoul of unforeseen diplomatic pressures. In 2008, The Dark Knight’s planned rollout in China was cancelled because of “cultural sensitivities” (likely to do with scenes set in Hong Kong involving a money-laundering character), which significantly hampered the film’s worldwide box-office take. But Crimson Peak’s problem is an even bigger one. The Film Bureau objects to films with distinctly spiritual content, because they “promote cults or superstition” in violation of the Communist Party’s secular principles—a major problem for a movie chock-full of ghosts.

There are, apparently, ways around the “no ghosts!” rule. One easy way is to explain that the people seeing visions of the dead were crazy, perhaps, or on drugs. The second Pirates of the Caribbean film, Dead Man’s Chest, was banned in China because it had spirits swarming around, but Disney accordingly made cuts to the Chinese version of the series’ third film, At World’s End, to make it acceptable. Crimson Peak, though, is set in a haunted house literally teeming with ghosts—ghost babies, ghost brides, old lady ghosts, even main-character ghosts. The film can’t simply shake that off as a bad dream, and so, even though the film has been hyped by two of China’s most popular film websites (according to The Hollywood Reporter), it may never get a legitimate release there.

This wouldn’t have been a problem even 10 years ago, when even the most successful Chinese releases only earned tens of millions of dollars—not much by Hollywood standards. But as the China Film Bureau started allowing more U.S. productions into theaters, more movie theaters were built around the country, and its annual box-office numbers exploded. In 2007, the highest grossing film in China was Transformers, which made $37 million. This year, it was Furious 7, which took $390 million. Del Toro’s Pacific Rim made $101 million in the United States in 2013 on a $190 million budget. But it took $111 million in China, nudging it into profitable territory. That kind of haul can rescue a film, even if it’s seen as a box-office failure in its home country.

Part of the reason for Pacific Rim’s success overseas was its inclusion of Chinese characters. Some blockbusters have started filming scenes that are inserted only in Chinese cuts, like Iron Man 3, which had a whole subplot that American audiences will never see. Reaction to the China-specific scenes, which were apparently inserted rather awkwardly, were reportedly mixed. But it helped carry the Marvel movie to an impressive $121 million take in the country. Other recent films, like Gravity, 2012, and Transformers: Age of Extinction, have benefited from including scenes that depict cooperation with Chinese characters.

Within a few years, the Chinese film market may overtake America as the world’s biggest, and such story tweaks might become more and more noticeable. It’s also possible the China Film Bureau will continue to relax its standards to keep up with changing trends and stay ahead of piracy within its borders. A more concerning trend to watch for will be whether Hollywood becomes reluctant to produce big-budget films that won’t sell overseas. As Birth Movies Death’s Devin Faraci points out, Marvel has Doctor Strange on its docket in 2016, which will be full of ghosts—maybe in a few years, that’ll be a harder sell for a big studio. Then again, they can always splice in a scene explaining that it was all a dream.