Meiotic crossovers (COs) are tightly regulated to ensure that COs on the same chromosome are distributed far apart ( crossover interference, COI) and that at least one CO is formed per homolog pair (CO homeostasis). CO formation is controlled in part during meiotic double-strand break (DSB) creation in Caenorhabditis elegans, but a second level of control must also exist because meiotic DSBs outnumber COs. We show that the anti-recombinase RTEL-1 is required to prevent excess meiotic COs, probably by promoting meiotic synthesis-dependent strand annealing. Two distinct classes of meiotic COs are increased in rtel-1 mutants, and COI and homeostasis are compromised. We propose that RTEL-1 implements the second level of CO control by promoting noncrossovers.