A lubricating composition for use in heavy duty diesel engines which is formulated to allow the use of organomolybdenum compounds but which overcomes the issue of Cu and/or Pb corrosion. The lubricant is characterized by having a synergistic additive composition comprising (A) a sulfur-free organo-molybdenum compound, (B) a sulfur-containing organo-molybdenum compound and (C) a triazole derivative prepared by reacting 1,2,4-triazole, a formaldehyde source and an amine; (A), (B) and (C) being present in an amount sufficient to allow the lubricating composition to pass the High Temperature Corrosion Bench Test ASTM D 6594 with respect to Cu and/or Pb corrosion.