Interpretation bias is often theorized to play a critical role in depression and social anxiety. To date, it remains unknown how interpretation bias exerts its toxic effects. Interpretation inflexibility may be an important determinant of how distorted interpretations affect emotional well-being. This study investigated interpretation bias and inflexibility in relation to depression severity and social anxiety. Participants (N = 212) completed a novel cognitive task that simultaneously measured bias and inflexibility in the interpretation of unfolding ambiguous situations. Depression severity was associated with increased negative and decreased positive interpretation biases. Social anxiety was associated with increased negative interpretation bias. Critically, both symptom types were related to reduced revision of negative interpretations by disconfirmatory positive information. These findings suggest that individuals with more severe depression or social anxiety make more biased and inflexible interpretations. Future work examining cognitive risk for depression and anxiety could benefit from examining both these factors.