diff --git a/include/gsl/pointers b/include/gsl/pointers
index 63e193e9..dd0f0682 100644
--- a/include/gsl/pointers
+++ b/include/gsl/pointers
@@ -75,7 +75,7 @@ using std::unique_ptr;
 // T must be a pointer type
 // - disallow construction from any type other than pointer type
 //
-template <class T, class = std::enable_if_t<std::is_pointer<T>::value>>
+template <class T, std::enable_if_t<std::is_pointer<T>::value, bool> = true>
 using owner = T;
 
 //