Cooperation in nature is ubiquitous, but is susceptible to social cheats who pay little or no cost of cooperation yet reap the benefits. The effect such cheats have on reducing population productivity suggests that there is selection for cooperators to mitigate the adverse effects of cheats. While mechanisms have been elucidated for scenarios involving a direct association between producer and cooperative product, it remains unclear whether cooperators can suppress cheating in an anonymous public goods scenario, whereby cheats cannot be directly identified. Here, we investigate the real-time evolutionary response of cooperators to cheats when cooperation is mediated by a diffusible public good; the production of iron-scavenging siderophores by Pseudomonas aeruginosa. We find that siderophore-producing cooperators evolved in the presence of a high frequency of non-producing cheats become more resilient to cheating by evolving reduced siderophore production, at no obvious cost to population productivity. Novel morphotypes, appeared independently in 5/6 cheat-adapted populations, exhibiting increased and reduced production of the toxin pyocyanin and the siderophore pyoverdine, respectively. These morphotypes were characterised by large deletions in lasR and rsaL genes. Finally, we demonstrate that the iron-reducing capabilities of pyocyanin may have contributed to the prevalence of these novel morphotypes in cheat-adapted populations.