diff --git a/include/gsl/pointers b/include/gsl/pointers
index bc6a91c..7afed1c 100644
--- a/include/gsl/pointers
+++ b/include/gsl/pointers
@@ -272,13 +272,13 @@ auto make_strict_not_null(T&& t) {
     return strict_not_null<std::remove_cv_t<std::remove_reference_t<T>>>{std::forward<T>(t)};
 }
 
-#if (defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L))
+#if ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
 
 // deduction guides to prevent the ctad-maybe-unsupported warning
 template <class T> not_null(T) -> not_null<T>;
 template <class T> strict_not_null(T) -> strict_not_null<T>;
 
-#endif // (defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L))
+#endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
 
 } // namespace gsl