We consider a uniform-price procurement auction with indivisible units and private independent costs. We find an explicit solution for a Bayesian Nash equilibrium, which is unique if demand shocks are sufficiently evenly distributed. The equilibrium has a price instability in the sense that a minor change in a supplier's realized cost can result in a drastic change in the market price. We quantify the resulting volatility and show that it is reduced as the size of indivisible units decreases. In the limit, the equilibrium converges to the Supply Function Equilibrium (SFE) for divisible goods if costs are common knowledge.