diff --git a/corsika/framework/geometry/QuantityVector.hpp b/corsika/framework/geometry/QuantityVector.hpp
index 57d09c29eb5c4684ead155ba2d8a7546f99abf6c..2c951a52b1c3c9a4437bae7c98e770542c430c4b 100644
--- a/corsika/framework/geometry/QuantityVector.hpp
+++ b/corsika/framework/geometry/QuantityVector.hpp
@@ -87,7 +87,7 @@ namespace corsika {
 
     auto operator+=(QuantityVector<TDimension> const& pQVec);
 
-    auto& operator-=(QuantityVector<TDimension> const& pQVec);
+    auto operator-=(QuantityVector<TDimension> const& pQVec);
 
     auto operator-() const;