diff --git a/tests/notnull_tests.cpp b/tests/notnull_tests.cpp
index 47f5ac2..d9e0709 100644
--- a/tests/notnull_tests.cpp
+++ b/tests/notnull_tests.cpp
@@ -46,16 +46,12 @@
 #include <string>    // for basic_string, operator==, string, operator<<
 #include <typeinfo>  // for type_info
 
-namespace gsl
-{
-struct fail_fast;
-} // namespace gsl
-
 using namespace gsl;
 
 namespace
 {
 static constexpr char deathstring[] = "Expected Death";
+} //namespace
 
 struct MyBase
 {
@@ -149,7 +145,6 @@ GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
 bool helper_const(not_null<const int*> p) { return *p == 12; }
 
 int* return_pointer() { return nullptr; }
-} //namespace
 
 TEST(notnull_tests, TestNotNullConstructors)
 {