diff --git a/include/gsl/gsl_byte b/include/gsl/gsl_byte
index 1e2e3be..7155210 100644
--- a/include/gsl/gsl_byte
+++ b/include/gsl/gsl_byte
@@ -30,15 +30,15 @@
 
 #ifndef GSL_USE_STD_BYTE
 // this tests if we are under MSVC and the standard lib has std::byte and it is enabled
-#if _MSC_VER >= 1911 && (!defined(_HAS_STD_BYTE) || _HAS_STD_BYTE)
+#if defined(_HAS_STD_BYTE) && _HAS_STD_BYTE
 
 #define GSL_USE_STD_BYTE 1
 
-#else // _MSC_VER >= 1911 && (!defined(_HAS_STD_BYTE) || _HAS_STD_BYTE)
+#else // defined(_HAS_STD_BYTE) && _HAS_STD_BYTE
 
 #define GSL_USE_STD_BYTE 0
 
-#endif // _MSC_VER >= 1911 && (!defined(_HAS_STD_BYTE) || _HAS_STD_BYTE)
+#endif // defined(_HAS_STD_BYTE) && _HAS_STD_BYTE
 #endif // GSL_USE_STD_BYTE
 
 #else // _MSC_VER
diff --git a/tests/unittest-cpp b/tests/unittest-cpp
new file mode 160000
index 0000000..dc6b908
--- /dev/null
+++ b/tests/unittest-cpp
@@ -0,0 +1 @@
+Subproject commit dc6b90838014ab985bf3cd74ac17ad9d00e1fbcb