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. NH2CHO, NH2CHO nu(12) = 1, (NH2CHO)-C-13, CH3C(O)-NH2 nu = 0, 1, CH2DOH, CH3CHO, and CH3C(O)CH3 are securely detected, while trans-NHDCHO, NH2CDO, CH3NHCHO nu = 0, 1, CH3COOH, and HOCH2CHO are tentatively identified. The results of this work are compared with detections presented in the literature. A uniform CH3C(O)NH2/NH2CHO ratio is found for a group of interstellar sources with vast physical differences. A similar ratio is seen for CH3NHCHO, based on a smaller data sample. The D/H ratio of NH2CHO is about 1-3% and is close to values found in the low-mass source IRAS 16293-2422B. The formation of CH3C(O)NH2 and NH2CHO 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 NH2CHO 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.