Sustainable innovation is essential for companies to stay in competition. The first phase of sustainable innovation is idea generation. Ideas for improvement can come from all employees, among whom employees that operate machines. The problem is that companies that strive for sustainable innovation often do not use the potential of their operators’ ideas for improvement. Therefore, this research aims to gain insight in how companies that strive for sustainable innovation can facilitate operators to display promotive voice. When operators share their ideas for improvement, this is called promotive voice. This leads to the research question: How can changes in the organizational context increase the probability that operators display promotive voice in companies that strive for sustainable innovation? Sub-questions are (i) What stimulates and limits promotive voice, according to literature? (ii) To what extent do operators, team leaders and management at Van Houtum B.V. find sustainability an important motive for improvement? (iii) To what extent do operators at Van Houtum B.V. perceive barriers and stimulants to display promotive voice? (iv) How can Van Houtum B.V. increase the likelihood that operators display promotive voice by changing the organizational context? This research question will be answered for one case company, by performing a design-based research. A theoretical framework is constructed and applied to this case study. An intervention aims to change an element of the organizational context. The effect of this intervention is used to reflect on the theoretical framework. According to the theoretical framework, companies that strive for sustainable innovation can increase the likelihood that operators display promotive voice by influencing a set of individual and contextual constructs, or by influencing how important their employees value different motives for an idea. (A motive for an idea is how important the individual assesses the envisioned outcome of the idea.) At the case company, eight motives for an idea were identified; to make work processes safer, more sustainable, cheaper, cleaner, easier, faster, give more production, or produce products with better quality. According to importance, respondents ranked the motive more sustainable on the third place, out of eight. Besides, operators appeared to experience many barriers and stimulants for promotive voice, of which the greatest barrier was the feeling that their ideas are not heard. An intervention that aimed to reduce this barrier indeed resulted in an increased likelihood that operators display promotive voice, but this effect was limited. According to team leaders, the likelihood that operators display promotive voice had slightly increased, because operators felt more heard. Yet, operators did not notice this change. In conclusion: In theory, there are many starting points for companies to increase the likelihood that operators display promotive voice, but in practice it is not easy to effectively change the organizational context in favor of promotive voice. The revised theoretical framework replaced individual and contextual constructs by critical variables for promotive voice. By validating `being heard' as a critical variable and identifying more critical variables, further research can develop a model that describes the decision of individuals to display promotive voice.