diff --git a/FWCore/Utilities/interface/RunningAverage.h b/FWCore/Utilities/interface/RunningAverage.h
index c60d51fbbb83d..8a5564cac7cfe 100644
--- a/FWCore/Utilities/interface/RunningAverage.h
+++ b/FWCore/Utilities/interface/RunningAverage.h
@@ -29,7 +29,7 @@ namespace edm {
 
     int upper() const {
       auto lm = mean();
-      return lm += (std::abs(m_buffer[0] - lm) + std::abs(m_buffer[N / 2] - lm));
+      return lm + (std::abs(m_buffer[0] - lm) + std::abs(m_buffer[N / 2] - lm));
     }  // about 2 sigma
 
     void update(unsigned int q) {