Can issue linkage, the combining of multiple issues into a single agreement, enhance the credibility of an agreement? I use the alliance relations of buffer states (states located between two recently or currently warring rivals) to test the claim that issue linkage enhances compliance with treaty obligations. The alliance relations of buffer states create a "hard case" for treaty compliance because, by being prone to invasion and occupation, buffer states have difficulties inducing states to remain committed to an alliance agreement. Hence, if linkage provisions can enhance the credibility of alliance commitments for buffer states, then linkage provisions should improve treaty compliance in nearly any context. I find that buffer states in alliances with trade provisions experience fewer opportunistic violations of the alliance terms, avoid occupation and invasion at a higher rate, and experience fewer third-party attacks than buffer states in other alliance arrangements.