1339 Désagneauxa, provisional designation 1934 XB, is an asteroid from the outer region of the asteroid belt, about 23 kilometers in diameter. It was discovered on 4 December 1934 by French astronomer Louis Boyer at the Algiers Observatory in Algeria, North Africa. The body was independently discovered, just a few nights later, by the Russian and Belgian astronomers, Grigory Neujmin and Eugène Delporte, at the Crimean Simeiz and Belgian Uccle Observatory, respectively. The discoverer, Louis Boyer, named the asteroid in honour of his brother-in-law.