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Abstract 46P/Wirtanen is a Jupiter-family comet, probably originating from the solar system’s Kuiper Belt, that now resides on a 5.4 yr elliptical orbit. During its 2018 apparition, comet 46P passed unusually close to the Earth (within 0.08 au), presenting an outstanding opportunity for close-up observations of its inner coma. Here we present observations of HCN, H¹³CN, and HC¹⁵N emission from 46P using the Atacama Compact Array. The data were analyzed using the SUBLIME non-LTE radiative transfer code to derive¹²C/¹³C and¹⁴N/¹⁵N ratios. The HCN/H¹³CN ratio is found to be consistent with a lack of significant¹³C fractionation, whereas the HCN/HC¹⁵N ratio of 68 ± 27 (using our most conservative 1σuncertainties), indicates a strong enhancement in¹⁵N compared with the solar and terrestrial values. The observed¹⁴N/¹⁵N ratio is also significantly lower than the values of ∼140 found in previous comets, implying a strong¹⁵N enrichment in 46P’s HCN. This indicates that the nitrogen in Jupiter-family comets could reach larger isotopic enrichments than previously thought, with implications for the diversity of¹⁴N/¹⁵N ratios imprinted into icy bodies at the birth of the solar system.