diff --git a/include/etl/adapters/diagonal.hpp b/include/etl/adapters/diagonal.hpp
index 07fea0e2..2e308e25 100644
--- a/include/etl/adapters/diagonal.hpp
+++ b/include/etl/adapters/diagonal.hpp
@@ -114,8 +114,8 @@ struct diagonal_matrix final : adapter<Matrix>, iterable<const diagonal_matrix<M
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template <typename E>
-    diagonal_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type> {
+    template <convertible_expr<value_type> E>
+    diagonal_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is diagonal
         if (!is_diagonal(e)) {
             throw diagonal_exception();
diff --git a/include/etl/adapters/hermitian.hpp b/include/etl/adapters/hermitian.hpp
index 9fe958f8..f08bf089 100644
--- a/include/etl/adapters/hermitian.hpp
+++ b/include/etl/adapters/hermitian.hpp
@@ -138,8 +138,8 @@ struct hermitian_matrix final : adapter<Matrix>, iterable<const hermitian_matrix
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template <typename E>
-    hermitian_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type> {
+    template <convertible_expr<value_type> E>
+    hermitian_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is hermitian
         if (!is_hermitian(e)) {
             throw hermitian_exception();
diff --git a/include/etl/adapters/lower.hpp b/include/etl/adapters/lower.hpp
index 9eda147e..e8f1df94 100644
--- a/include/etl/adapters/lower.hpp
+++ b/include/etl/adapters/lower.hpp
@@ -114,8 +114,8 @@ struct lower_matrix final : adapter<Matrix>, iterable<const lower_matrix<Matrix>
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template <typename E>
-    lower_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type> {
+    template <convertible_expr<value_type> E>
+    lower_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is lower triangular
         if (!is_lower_triangular(e)) {
             throw lower_exception();
diff --git a/include/etl/adapters/strictly_lower.hpp b/include/etl/adapters/strictly_lower.hpp
index 5dd8451d..0d2d6455 100644
--- a/include/etl/adapters/strictly_lower.hpp
+++ b/include/etl/adapters/strictly_lower.hpp
@@ -115,8 +115,8 @@ struct strictly_lower_matrix final : adapter<Matrix>, iterable<const strictly_lo
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template <typename E>
-    strictly_lower_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type>{
+    template <convertible_expr<value_type> E>
+    strictly_lower_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is strictly lower triangular
         if (!is_strictly_lower_triangular(e)) {
             throw strictly_lower_exception();
diff --git a/include/etl/adapters/strictly_upper.hpp b/include/etl/adapters/strictly_upper.hpp
index 375bdb64..8e4a1c89 100644
--- a/include/etl/adapters/strictly_upper.hpp
+++ b/include/etl/adapters/strictly_upper.hpp
@@ -114,8 +114,8 @@ struct strictly_upper_matrix final : adapter<Matrix>, iterable<const strictly_up
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template<typename E>
-    strictly_upper_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type> {
+    template<convertible_expr<value_type> E>
+    strictly_upper_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is strictly upper triangular
         if (!is_strictly_upper_triangular(e)) {
             throw strictly_upper_exception();
diff --git a/include/etl/adapters/symmetric.hpp b/include/etl/adapters/symmetric.hpp
index d6352a43..bda47f81 100644
--- a/include/etl/adapters/symmetric.hpp
+++ b/include/etl/adapters/symmetric.hpp
@@ -138,8 +138,8 @@ struct symmetric_matrix final : adapter<Matrix>, iterable<const symmetric_matrix
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template <typename E>
-    symmetric_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type> {
+    template <convertible_expr<value_type> E>
+    symmetric_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is symmetric
         if (!is_symmetric(e)) {
             throw symmetric_exception();
diff --git a/include/etl/adapters/uni_upper.hpp b/include/etl/adapters/uni_upper.hpp
index 9915c187..c67ac39b 100644
--- a/include/etl/adapters/uni_upper.hpp
+++ b/include/etl/adapters/uni_upper.hpp
@@ -109,8 +109,8 @@ struct uni_upper_matrix final : adapter<Matrix>, iterable<const uni_upper_matrix
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template <typename E>
-    uni_upper_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type> {
+    template <convertible_expr<value_type> E>
+    uni_upper_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is uni upper triangular
         if (!is_uni_upper_triangular(e)) {
             throw uni_upper_exception();
diff --git a/include/etl/adapters/upper.hpp b/include/etl/adapters/upper.hpp
index 255d6756..c4ec2a4c 100644
--- a/include/etl/adapters/upper.hpp
+++ b/include/etl/adapters/upper.hpp
@@ -114,8 +114,8 @@ struct upper_matrix final : adapter<Matrix>, iterable<const upper_matrix<Matrix>
      * \param e The ETL expression to get the values from
      * \return a reference to the fast matrix
      */
-    template <typename E>
-    upper_matrix& operator=(E&& e) noexcept(false) requires convertible_expr<E, value_type> {
+    template <convertible_expr<value_type> E>
+    upper_matrix& operator=(E&& e) noexcept(false) {
         // Make sure the other matrix is upper triangular
         if (!is_upper_triangular(e)) {
             throw upper_exception();
diff --git a/include/etl/concepts.hpp b/include/etl/concepts.hpp
index 80dc85a0..cfb2b5ca 100644
--- a/include/etl/concepts.hpp
+++ b/include/etl/concepts.hpp
@@ -117,7 +117,7 @@ concept matrix = etl_expr<T> && decay_traits<T>::dimensions() > 1;
 template <typename T>
 concept fast_matrix_c = fast<T> && matrix<T>;
 
-template <typename E, typename T>
+template <typename T, typename E>
 concept same_dimensions = etl_expr<T> && decay_traits<T>::dimensions() == decay_traits<E>::dimensions();
 
 template <typename T>