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We present a detailed ac susceptibility investigation of the fluctuation regime in the insulating cubic helimagnet Cu2OSeO3. For magnetic fields mu H-0 >= 200 mT, and over a wide temperature (T) range, the system behaves according to the scaling relations characteristic of the classical three-dimensional Heisenberg model. For lower magnetic fields, the scaling is preserved only at higher T and becomes renormalized in a narrow-T range above the transition temperature. Contrary to the well-studied case of MnSi, where the renormalization has been interpreted within the Brazovskii theory, our analysis of the renormalization at H = 0 shows the fluctuation regime in Cu2OSeO3 to lie closer to that expected within the Wilson-Fischer scenario.