diff --git a/dune/istl/io.hh b/dune/istl/io.hh
index 71420ea596eb3b47438d52bd48a14fda4f6b642f..d7bd69c2200e0c214675e7a78d22d90041da20a1 100644
--- a/dune/istl/io.hh
+++ b/dune/istl/io.hh
@@ -147,14 +147,14 @@ namespace Dune {
    * #include <dune/istl/io.hh>
    * \endcode
    */
-  template<class K>
+  template<class K,
+    std::enable_if_t<Dune::IsNumber<K>::value, int> = 0>
   void print_row (std::ostream& s, const K& value,
                   [[maybe_unused]] typename FieldMatrix<K,1,1>::size_type I,
                   [[maybe_unused]] typename FieldMatrix<K,1,1>::size_type J,
                   [[maybe_unused]] typename FieldMatrix<K,1,1>::size_type therow,
                   int width,
-                  [[maybe_unused]] int precision,
-                  [[maybe_unused]] typename std::enable_if_t<Dune::IsNumber<K>::value>* sfinae = nullptr)
+                  [[maybe_unused]] int precision)
   {
     s << " ";         // space in front of each entry
     s.width(width);   // set width for each entry anew