Significance Cellular accumulation of reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) is associated with stress responses as well as aging. The reactive nature of ROS marks these molecules as a serious threat to cell integrity. Consequently, eukaryotic cells deploy numerous antioxidant enzymes that detoxify ROS to protect them from ROS-induced damage to proteins. Although the importance of antioxidant enzymes is well understood, how these proteins avoid becoming damaged in the hostile, ROS-rich environments in which they function remains unknown. We show that in plant cells the oxidoreductase Nucleoredoxin 1 (NRX1) protects antioxidant enzymes such as catalase from ROS-induced oxidation. Importantly, this protective effect of NRX1 boosted the H 2 O 2 detoxification capacity of catalase, thereby protecting the plant cell from oxidative stress.