Angular distributions of the decay B0 → K∗0 μ+ μ− are studied using a sample of proton-proton collisions at sqrt(s) = 8 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb^−1. An angular analysis is performed to determine the P 1 and P'5 parameters, where the P'5 parameter is of particular interest because of recent measurements that indicate a potential discrepancy with the standard model predictions. Based on a sample of 1397 signal events, the P1 and P'5 parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with predictions based on the standard model