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Description: In conversations, interlocutors manage to concurrently perform highly related processes: comprehension and speech planning. We wanted to disentangle neural signatures of these processes using event related potentials (ERPs), to investigate interference of speech planning on comprehension. In two experiments, Dutch speakers listened to sentences that ended with expected or unexpected target words. Participants’ task was to either name pictures belonging to a fruit or vegetable category, or to stay quiet when pictures of the other category appeared. In Experiment 1, the pictures appeared two seconds after the target word onset. As expected, we found a strong N400 effect when the word planning began after the comprehension was completed. In Experiment 2, the pictures appeared shortly before the target words. We predicted that the N400 effect would be smaller in the plan compared to no-plan condition. Surprisingly, we did not find the interaction between expectancy and planning. Interestingly, we found smaller N400 effect in Experiment 2 compared to Experiment 1. This pattern of results indicates that conceptual preparation or the decision to speak (taking place in both plan and no-plan conditions) interfere with comprehension, rather than processes specific to word planning.