diff --git a/include/xlnt/utils/optional.hpp b/include/xlnt/utils/optional.hpp
index e019f316..f19bc286 100644
--- a/include/xlnt/utils/optional.hpp
+++ b/include/xlnt/utils/optional.hpp
@@ -37,15 +37,8 @@ namespace xlnt {
 template <typename T>
 class optional
 {
-#if _MSC_VER <= 1900 // v14, visual studio 2015
+#if defined(_MSC_VER) && _MSC_VER <= 1900 // v14, visual studio 2015
 #define XLNT_NOEXCEPT_VALUE_COMPAT(...) (false)
-    using ctor_copy_T_noexcept = std::false_type;
-    using ctor_move_T_noexcept = std::false_type;
-    using copy_ctor_noexcept = ctor_copy_T_noexcept;
-    using move_ctor_noexcept = ctor_move_T_noexcept;
-    using set_copy_noexcept_t = std::false_type;
-    using set_move_noexcept_t = std::false_type;
-    using clear_noexcept_t = std::false_type;
 #else
 #define XLNT_NOEXCEPT_VALUE_COMPAT(...) (__VA_ARGS__)
     using ctor_copy_T_noexcept = typename std::conditional<std::is_nothrow_copy_constructible<T>{}, std::true_type, std::false_type>::type;
diff --git a/source/CMakeLists.txt b/source/CMakeLists.txt
index 2ea048d3..11e3593c 100644
--- a/source/CMakeLists.txt
+++ b/source/CMakeLists.txt
@@ -41,6 +41,7 @@ elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-padded") # ignore padding warnings
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-documentation-unknown-command") # ignore unknown commands in Javadoc-style comments
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unknown-pragmas") # ignore Windows and GCC pragmas
+  set CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unknown-warning-option") # ignore Windows and GCC pragmas
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-float-equal") # don't warn on uses of == for fp types
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-newline-eof") # no longer an issue with post-c++11 standards which mandate include add a newline if neccesary
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-covered-switch-default") # default is often added to switches for completeness or to cover future alternatives