The execution of complex working memory tasks often requires various cognitive control operations on stored content. Here we focus on the integration operation – defined as merging the outcome of subtask processing with additional information actively maintained before and during subtask execution. In prior work, we identified the anterior prefrontal cortex as critical for integration during mental arithmetic. Here we replicate and extend these results in an adapted mental arithmetic task that enabled examination of the detailed temporal dynamics of the anterior prefrontal activation. We find that this region is involved in the preparation for integration, possibly by ensuring that goal-relevant information is maintained in an accessible form, while at the same time protected from subtask interference.