Preprint of paper published in: ICSM 2008 - IEEE International Conference on Software Maintenance, 28 September-4 October 2008; doi:10.1109/ICSM.2008.4658076 In spite of the widespread use of coding standards and tools enforcing their rules, there is little empirical evidence supporting the intuition that they prevent the introduction of faults in software. Not only can compliance with a set of rules having little impact on the number of faults be considered wasted effort, but it can actually result in an increase in faults, as any modification has a non-zero probability of introducing a fault or triggering a previously concealed one. Therefore, it is important to build a body of empirical knowledge, helping us understand which rules are worthwhile enforcing, and which ones should be ignored in the context of fault reduction. In this paper, we describe two approaches to quantify the relation between rule violations and actual faults, and present empirical data on this relation for the MISRA C 2004 standard on an industrial case study.