We present two modifications to the qualitative simulation algorithm QSIM, which improve its performance in reasoning tasks involving infinite values and infinite time. The first modification corrects an error in the multiplication filter which causes the algorithm to miss certain real solutions of the simulated equation. The soundness property, which is essential for qualitative simulators, is therefore restored to QSIM. The second modification augments the temporal attribute computation routine and results in better identification of infinite time intervals by the algorithm. This, in turn, helps our modified algorithm to successfully eliminate some additional spurious behaviors. Several famous examples from the qualitative reasoning literature are handled with increased predictive accuracy by the new algorithm.