We study the synchronization of two nonidentical oscillators with nonvanishing nonisochronicity under the presence of uncorrelated Gaussian noise. To measure the amount of synchronization we calculate the evolution of the phase difference. Without coupling both oscillators rotate with different natural frequencies. Due to the action of coupling this frequency difference is reduced until finally, at a critical coupling strength, synchronization sets in. Under the presence of uncorrelated noise the observed frequency differences is still a monotonically decreasing function of coupling strength but can never become zero due to noise induced phase slips. Here, we show that this usual picture of the transition to synchronization is strongly modified when the oscillators are nonisochronous. In this case the onset of coupling can have different effects and may enlarge or even invert the natural frequency difference of the uncoupled oscillators. Our results can be explained in terms of a noisy particle in a tilted potential.