Twitter is being criticised for failing to show any photos under the bisexual hashtag.
Some are calling it bi-erasure, as photo results for "lesbian" and "gay" still exist.
Users are pointing out that when you search #bisexual, a message appears on the photos tab stating: "The term you entered did not bring up any results."
Twitter has yet to comment on the reason why the photos don't show up.
Image caption The message a user gets when you type bisexual into the photo search field
Kate Harrad, of campaign group The Bisexual Index, tells Newsbeat that bisexual people have "historically been hypersexualised and associated with porn and promiscuity".
"Every bi-activist knows the problems of trying to search for bi-content on the web and some public wifi systems block it altogether, even when it's nothing to do with sex, because bisexual is seen as a dodgy word in itself.
"This is why Twitter needs to be very sensitive to any filtering that reduces access to bi content, and very aware of the problem of bisexual erasure."