Writing from sources requires the processing of both external (documentary) and internal (long-term memory; LTM) sources of information, which can sometimes interfere with each other. We hypothesised that writers with high working memory (WM) capacity would resolve interference faster than those with low-capacity WM. However, results showed that writing pause duration was shorter for low-capacity writers. This result suggests that when WM resources are limited, access to domain knowledge in LTM is restricted, thereby avoiding interference between the two sources. Results are discussed within the broader context of text composition from sources and individual differences.