An angular analysis of B⁰d → K⁰(→K⁺π⁻)μ⁺μ⁻ is presented using 20.3 fb⁻¹ of pp collision data collected at √s = 8 TeV with the ATLAS experiment. The angular observables FL and S₃,₄,₅,₇,₈ were extracted in six bins of q², the invariant mass squared of the dimuon system, within the full range 0.04 < q² < 6.00 (GeV/c²)². The observables were determined from an unbinned maximum likelihood fit using four folded parameterisations of the full angular distribution. The fit results were used to obtain corresponding values for the optimised observables P₁ and P'₄,₅,₆,₈. The results presented are compatible with Standard Model predictions.