As state-sponsored disinformation is increasingly recognised as a threat to democratic societies, academic research has intensified efforts to explain individual-level susceptibility to disinformation and the effectiveness of countermeasures. This study contributes to this research by applying Psychological Reactance Theory to the study of how individuals react to Russian state-sponsored disinformation. Specifically, it examines whether trait reactance moderates the effect of source information on susceptibility to disinformation. A between-subject experimental survey study was conducted among Swedish-speaking participants over 18 years old. Participants read a news article from a Russian-controlled news site targeting European audiences. Participants were assigned to one of three groups, which received different information about the source prior to reading the article (no source information, neutral information about the source, or source information combined with a general recommendation from the Swedish Agency for Psychological Defence). Trait reactance was hypothesised to moderate the effect of different types of source information on susceptibility. No support is found for the hypothesised interaction effects. An unexpected finding is however a robust and statistically significant positive correlation between trait reactance and susceptibility to state-sponsored disinformation. This correlation is present for several aspects of susceptibility and is consistent across the three groups (i.e., did not depend on the type of source information). These findings indicate a potential avenue for further research on trait reactance as an explanatory factor in individual-level differences in susceptibility to disinformation.