Treating a subterranean formation with a composition including a maleic anhydride copolymer, an amine crosslinker, and a gelling agent. The maleic anhydride copolymer includes first repeat units I and II and at least one of second repeat units III and IV: where each R1 is independently-H, —O(C1-C5) alkyl, or —(C1-C5) alkyl; each R2 is independently-H, —O(C1-C5) alkyl, or —(C1-C5) alkyl; each R3 is independently —OH or —O−M1, each M1 is independently an alkali metal, an alkaline earth metal, an ammonium ion, or a quaternary ammonium ion; and each R4 is independently-NH2 or —OM1. The gelling agent includes at least one of: a calcium chelating agent, a calcium precipitating agent, a pH buffer, an agent reactive with hydroxide, and an acid generating agent, and promotes formation of a gel from the maleic anhydride copolymer and the amine crosslinker in contact with set cement.