We extend an L 2 energy gap result due to Theorem 2] and Parker [30, Proposition 2.2] for Yang-Mills connections on principal G-bundles, P , over closed, connected, four-dimensional, oriented, smooth manifolds, X, from the case of positive Riemannian metrics to the more general case of good Riemannian metrics, including metrics that are generic and where the topologies of P and X obey certain mild conditions and the compact Lie group, G, is SU (2) or SO(3). A 13 4.2. Completion of the proofs of Theorem 1 and Corollary 2 14 Appendix A. Uhlenbeck continuity of the least eigenvalue of d + A d +, * A with respect to the connection 15 References 22