Although practitioner literature asserts a link between an auditor’s quality control system and engagement-level audit outcomes, prior archival evidence has struggled to identify observable indicators in support of this claim. We identify an observable failure that is unambiguously attributable to the auditor – a mistake in the audit report identified by the SEC – as an office-level proxy for poor, office-level quality control systems. Audit report errors suggest a breakdown in the engagement’s quality review process, which we expect to signal broader quality control problems in the respective office. Consistent with this hypothesis, we find that clients of a Big Four office cited for an audit report error display lower financial reporting quality than do clients of offices not cited for errors. We document this pattern in abnormal accruals, report lag, and adverse opinions on internal controls. Further, the SEC comment appears to trigger increased auditor attention to the quality review; after the SEC exposes an audit report error, financial reporting quality improves in the clients of the culpable office. Our results suggest that audit firms’ internal quality mechanisms impact the quality of the financial reporting process. They also suggest that audit report errors may be used as a proxy for an office’s audit quality independent of its clients’ pre-audit inputs.