diff --git a/include/ghc/fs_std.hpp b/include/ghc/fs_std.hpp
index 9b54a0d..22e93fe 100644
--- a/include/ghc/fs_std.hpp
+++ b/include/ghc/fs_std.hpp
@@ -47,6 +47,7 @@ using ofstream = std::ofstream;
 using fstream = std::fstream;
 }
 #else
+#define GHC_WIN_WSTRING_STRING_TYPE
 #include <ghc/filesystem.hpp>
 namespace fs {
 using namespace ghc::filesystem;
diff --git a/include/ghc/fs_std_fwd.hpp b/include/ghc/fs_std_fwd.hpp
index 68dcb3e..40dee2a 100644
--- a/include/ghc/fs_std_fwd.hpp
+++ b/include/ghc/fs_std_fwd.hpp
@@ -50,6 +50,7 @@ using ofstream = std::ofstream;
 using fstream = std::fstream;
 }
 #else
+#define GHC_WIN_WSTRING_STRING_TYPE
 #define GHC_FILESYSTEM_FWD
 #include <ghc/filesystem.hpp>
 namespace fs {
diff --git a/include/ghc/fs_std_impl.hpp b/include/ghc/fs_std_impl.hpp
index 96f0f5c..4f6f1c0 100644
--- a/include/ghc/fs_std_impl.hpp
+++ b/include/ghc/fs_std_impl.hpp
@@ -40,6 +40,7 @@
 // header to work.
 //---------------------------------------------------------------------------------------
 #if !(defined(__cplusplus) && __cplusplus >= 201703L && defined(__has_include) && __has_include(<filesystem>))
+#define GHC_WIN_WSTRING_STRING_TYPE
 #define GHC_FILESYSTEM_IMPLEMENTATION
 #include <ghc/filesystem.hpp>
 #endif