diff --git a/src/algebra/TinyMatrix.hpp b/src/algebra/TinyMatrix.hpp
index bafd84bdc281f58c9e62e4fd312fe8dce183838b..9fd69705b96bf188e43f160ff0abdbf95592a3c1 100644
--- a/src/algebra/TinyMatrix.hpp
+++ b/src/algebra/TinyMatrix.hpp
@@ -174,12 +174,11 @@ public:
   }
 
   PASTIS_INLINE
-  constexpr volatile TinyMatrix& operator+=(const volatile TinyMatrix& A) volatile
+  constexpr void operator+=(const volatile TinyMatrix& A) volatile
   {
     for (size_t i=0; i<N*N; ++i) {
       m_values[i] += A.m_values[i];
     }
-    return *this;
   }
 
   PASTIS_INLINE
diff --git a/src/algebra/TinyVector.hpp b/src/algebra/TinyVector.hpp
index 417d26fadfa8badf208410910661dddb5f163d09..6d833e6b31b3aea0815280f36fd3d0ae89ba2a43 100644
--- a/src/algebra/TinyVector.hpp
+++ b/src/algebra/TinyVector.hpp
@@ -151,12 +151,11 @@ class TinyVector
   }
 
   PASTIS_INLINE
-  constexpr volatile TinyVector& operator+=(const volatile TinyVector& v) volatile
+  constexpr void operator+=(const volatile TinyVector& v) volatile
   {
     for (size_t i=0; i<N; ++i) {
       m_values[i] += v.m_values[i];
     }
-    return *this;
   }
 
   PASTIS_INLINE