is sstream really always required?

include/greeter.h

@@ -2,11 +2,6 @@
 
 #include <string>
 
-#if defined(_WIN32) || defined(WIN32)
-// apparently this is required to use strings in MSVC++
-#  include <sstream>
-#endif
-
 namespace greeter {
 
   enum class LanguageCode { EN, DE, ES, FR };

test/source/greeter.cpp

@@ -1,6 +1,8 @@
 #include <doctest/doctest.h>
 #include <greeter.h>
 
+#include <sstream>
+
 TEST_CASE("Greeter") {
   using namespace greeter;