The readback/hearback protocol is a communicative procedure used to minimize the risk of communication errors over the radio or telephone in high-risk environments. This protocol requires the receiver of a verbal instruction to repeat or 'read back' the instruction to the sender to ensure it has been heard correctly. It is a common assumption that a correct readback confirms that a receiver has understood an instruction. However, an operator can accurately repeat an instruction while concealing their lack of understanding of the instruction. Previous research has highlighted the importance of intonation as a prosodic cue to aid in the detection of non-understandings during readback/hearback exchanges over the radio. As deviations from the standard readback procedure occur frequently, it is unclear whether intonation is equally as useful in the detection of non-understandings when contained within a partial readback response. Using an international sample of hydroelectric power generation operators, the current study assessed whether the use of a full readback leads to a greater perception that the receiver has understood the instruction compared to a partial readback. It also examined the utility of intonation during perceptions of non-understanding upon hearing a full readback versus partial readback response. The results indicated that full readback responses attracted a greater assumption of understanding compared to partial readback responses (but only for native English speakers), and that intonation was only used to detect non-understandings during partial readback responses that lacked the semantic information contained within a full readback. Practical implications of the findings are discussed.