The abundant phyllosilicate and carbonate minerals characterizing most of the returned particles from asteroid Ryugu suggest a history of extensive aqueous alteration on its parent body1,2, similar to the rare, mineralogically altered, but chemically primitive CI (Ivuna-type) chondrite meteorites. Particle C0009 differs mineralogically from other Ryugu particles examined to date by containing anhydrous silicates at a level of ~0.5 vol% (Ito et al. submitted), and thus can help shed light on the original materials that constituted Ryugu’s protolith. In-situ oxygen isotope measurements of the most Mg-rich olivine and pyroxene in C0009 reveal two populations of ∆17O: −25‰ to −15‰ and −8‰ to −3‰, correlating well with the silicate morphologies similar to those seen in amoeboid olivine aggregates (AOAs)3–7 and chondrule phenocrysts8,9, respectively, abundant in less aqueously altered carbonaceous chondrites. This result represents the first discovery of olivine with ∆17O close to the solar value10 in either a CI chondrite or an asteroid of CI-chondrite characteristics and provides strong evidence that AOAs and Mg-rich chondrules accreted into Ryugu’s protolith. Our data also raise the possibility that the protoliths of CI and other carbonaceous chondrites incorporated similar anhydrous silicates.