LONDON (AP) — A set of the first four editions of William Shakespeare’s collected works is expected to sell for up to $6 million at auction next month.

Sotheby’s auction house announced the sale on Wednesday, Shakespeare’s 461st birthday. It said the May 23 sale will be the first time since 1989 that a set of the First, Second, Third and Fourth Folios has been offered at auction as a single lot.

The auction house estimated the sale price at between 3.5 million and 4.5 million pounds.

After Shakespeare’s death in 1616, his plays were collected into a single volume by his friends John Heminges and Henry Condell, actors and shareholders in the playwright’s troupe, the King’s Men.

The First Folio — fully titled “Mr. William Shakespeares Comedies, Histories & Tragedies” — contained 36 plays, of which half were published there for the first time. Without the book, scholars say, plays including “Macbeth,” “The Tempest” and “Twelfth Night” might have been lost. Sotheby’s called the volume “without question the most significant publication in the history of English literature.”

About 750 copies were printed in 1623, of which about 230 are known to survive.