This paper presents a technique to fix timing violations caused by process variations in FPGAs by adjusting the clock skews of flip-flops. This involves making the clock distribution network tunable by adding programmable delay elements to compensate for variations. We propose generic as well as chip-specific skew assignment schemes that are robust to variations. The two proposed schemes result in recovering about 80% and 82% of the failed chips respectively with conservative timing constraints. With more aggressive constraints, the corresponding numbers are 69% and 77% respectively. Our technique causes a 39% increase in the number of chips in the fast bin when speed-binning is performed. The area and power overhead associated with this technique are 3.5% and 5.6% respectively.