Author Mark Forsyth said he was in the London library working on a book when he logged onto the network to check a line from William Shakespeare's play, the BBC reported Wednesday.
Forsyth said he was shocked to find the network's filter blocked his access to the play's text due to "violent content."
A British Library spokesman blamed the facility's third-party WiFi service, which he said was newly installed at the time.
"The upgraded service has a web filter to ensure that inappropriate content cannot be viewed on-site," the spokesman said. "We've received feedback from a number of users about sites which were blocked, but shouldn't have been. We're in the process of tweaking the service to unblock these sites."
All but one of the major characters are killed in the Shakespeare tragedy -- by drowning, beheading, stabbing, poisoning and, in Act V, by a sword dipped in poison.