This work aims to constrain the abundances of interstellar amides, by searching for this group of prebiotic molecules in the intermediate-mass protostar Serpens SMM1-a. ALMA observations are conducted toward Serpens SMM1. A spectrum is extracted toward the SMM1-a position and analyzed with the CASSIS line analysis software for the presence of characteristic rotational lines of a number of amides and other molecules. NH ₂CHO, NH ₂CHO ν ₁₂= 1, NH ₂ ¹³CHO, CH ₃C(O)NH ₂ν = 0, 1, CH ₂DOH, CH ₃CHO, and CH ₃C(O)CH ₃are securely detected, while trans-NHDCHO, NH ₂CDO, CH ₃NHCHO ν = 0, 1, CH ₃COOH, and HOCH ₂CHO are tentatively identified. The results of this work are compared with detections presented in the literature. A uniform CH ₃C(O)NH ₂/NH ₂CHO ratio is found for a group of interstellar sources with vast physical differences. A similar ratio is seen for CH ₃NHCHO, based on a smaller data sample. The D/H ratio of NH ₂CHO is about 1-3% and is close to values found in the low-mass source IRAS 16293-2422B. The formation of CH ₃C(O)NH ₂and NH ₂CHO is likely linked. Formation of these molecules on grain surfaces during the dark cloud stage is a likely scenario. The high D/H ratio of NH ₂CHO is also seen as an indication that these molecules are formed on icy dust grains. As a direct consequence, amides are expected to be present in the most pristine material from which planetary systems form, thus providing a reservoir of prebiotic material.