We present a genome assembly from an individual male Idaea aversata (the Riband Wave; Arthropoda; Insecta; Lepidoptera; Geometridae). The genome sequence is 437 megabases in span. The whole assembly is scaffolded into 30 chromosomal pseudomolecules, including the assembled Z sex chromosome. The mitochondrial genome has also been assembled and is 17.5 kilobases in length. Gene annotation of this assembly on Ensembl identified 10,165 protein coding genes.