Whistleblowing is an important fraud-prevention mechanism in public sector organisations, yet the formal availability of a whistleblowing system (WBS) does not necessarily ensure its practical use. This study examines how bureaucratic actors make sense of whistleblowing within a Javanese public bureaucracy and how these interpretations shape responses to suspected organisational irregularities. An interpretive qualitative single-case study was conducted in an anonymised provincial inspectorate in Indonesia, involving five participants comprising two WBS administrators and three users or prospective users. Data were collected through semi-structured interviews, observations, naturally occurring conversations, and institutional documents, and were analysed using reflexive thematic analysis informed primarily by sensemaking theory. The findings identified three interrelated themes: a gap between awareness and formal reporting; negotiation of cultural and religious-ethical considerations; and the interaction of formal reporting expectations with relational and cultural logics. Participants interpreted reporting through concerns about hierarchy, interpersonal relationships, stigma, evidential sufficiency, fitnah, confidentiality, and institutional follow-up. Consequently, responses included formal reporting, informal reminders, internal resolution, delayed action, and silence. The study introduces negotiated meaning as a case-generated analytical label for explaining how formal integrity expectations are reconciled with social and moral considerations. Strengthening WBS implementation therefore requires not only procedural safeguards, confidentiality, and credible follow-up, but also organisational legitimacy that enables reporting to be understood as fair, responsible, and socially defensible.