Say my brother in Latin

From Genesis 4, 9 - King James Version:

"And the LORD said unto Cain, Where is Abel thy brother?

And he said, I know not: Am I my brother's keeper?" In St. Jerome's Latin version, The Vulgate, this is:

"et ait Dominus ad Cain ubi est Abel frater tuus qui respondit nescio num custos fratris mei sum?" "Your brother's keeper" would be "custos fratris tui".