Hyperactive error monitoring is a robust neurocognitive characteristic in obsessive-compulsive disorder (OCD). Yet, relatively little is known about the flexibility and potential moderators of error monitoring in OCD. The current study investigates error monitoring in 30 healthy participants and 28 patients with OCD using a flanker task in 2 conditions either emphasizing speed or accuracy. Results indicate that no group difference is observable in error-related negativity (ERN) under the accuracy-focused condition. Both groups show an ERN attenuation in the speed condition; however, this reduction is larger in healthy controls leading to pronounced group differences in the speed-focused condition. Similarly, receiver operating characteristic analyses yield an area under the curve (AUC) of .62 in the accuracy-focused condition, whereas under speed instruction an AUC of .85 suggests a marked increase in classification accuracy. Behavioral results and results from a drift-diffusion model of decision making indicate a more cautious response strategy and less adaptability to experimental manipulations in OCD. Overall, results suggest that the observed increases in error-related neural activity in OCD might stem from a reduced flexibility and diminished ability to disengage from an accuracy-oriented, error-avoidant response style. Further, the present results suggest that emphasizing speed in experimental instructions may lead to a better neural differentiation between patients with OCD and healthy controls which has important implications for the use of the ERN as a risk indicator. (PsycINFO Database Record (c) 2019 APA, all rights reserved).