Flow, a psychological state of intense engagement in and enjoyment of an activity, can arise during both solitary and socially interactive experiences. In the literature, whereas people high in extraversion have difficulty achieving flow in solitude, those with an autotelic personality-a combination of traits that make people prone to flow-readily experience flow in both solitary and interactive conditions. In this pre-registered experiment, we investigated whether autotelic personality mitigates the negative association between solitary flow and extraversion. Participants and their romantic partners (final N = 368) played the game Perfection™ in three conditions (order was counterbalanced): alone (solitary condition), in the presence of their partner without interaction (mere-presence condition), and collaboratively (interactive condition). There were independent, positive main effects of extraversion and autotelic personality on flow experience in mere-presence and interactive conditions. However, the positive effect of extraversion on solitary flow was only significant among participants with high (vs. low) autotelic personality. In all conditions, flow experience was associated with greater low-arousal positive affect and lesser high-arousal negative affect. The findings shed light on the role of personality in promoting solitary flow experiences, and particularly how traits might interact to determine optimal and non-optimal conditions for achieving flow.