We create proxies for constrained supply of lendable shares by combining unique data on loan fees, stock lending activity, and failures to deliver to examine how often contrarian short sale strategies are affected by constraints. We find that constraints, as captured by our measures, clearly affect the strategies of NYSE and Nasdaq short sellers. In some cases 30%-40% of the cross-section experiences a significant reduction in the contrarian response of short sellers to past returns. However, only for extremely high levels of our constraint measures (top 1%) is contrarian behavior by short sellers completely eliminated. We also find that high minus low daily short selling activity portfolios produce abnormal returns for both constrained and unconstrained stocks.