Fluid loss control additives for a cement slurry are provided. An exemplary fluid loss control additive includes a copolymer containing 2-acrylamido-2-methylpropane sulfonic acid monomer units and acryloylmorpholine monomer units, and a graft copolymer. The graft copolymer contains a humate and, grafted onto the humate, a side-chain polymer containing at least one of acrylamide monomer units, acryloylmorpholine monomer units, acrylic acid monomer units, and 2-acrylamido-2-methylpropane sulfonic acid monomer units.