Extensive Monte Carlo simulation has been performed on a 2D modified XY model which behaves like a dense defect system. Topological defects are shown to introduce disorders in the system which makes the helicity modulus jump non-universal. The results corroborate the experimental observation of non-universal jump of the superconducting density in high-$T_c$ superconducting films.Comment: 4 pages, 5 figures, double column, Accepted for publication as a Rapid Communication in Phys. Rev. E (In Press
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