diff --git a/rtengine/LUT.h b/rtengine/LUT.h
index a0b078d79..6ec6447d6 100644
--- a/rtengine/LUT.h
+++ b/rtengine/LUT.h
@@ -266,6 +266,7 @@ public:
                 data[i] += rhs.data[i];
             }
         }
+        return *this;
     }
 
     // use with integer indices