diff --git a/lib/external/getenv.hpp b/lib/external/getenv.hpp
index a31992a18..6b2960371 100644
--- a/lib/external/getenv.hpp
+++ b/lib/external/getenv.hpp
@@ -2,6 +2,7 @@
 #define ISAAC_TOOLS_GETENV
 
 #include <string>
+#include <cstdlib>
 
 namespace isaac
 {
diff --git a/lib/external/to_string.hpp b/lib/external/to_string.hpp
index 74ac81667..d963f4d2a 100644
--- a/lib/external/to_string.hpp
+++ b/lib/external/to_string.hpp
@@ -13,7 +13,7 @@ template<class T>
 inline std::string to_string ( T const t )
 {
 
-#ifdef _GLIBCXX_HAVE_BROKEN_VSWPRINTF
+#ifdef __CYGWIN__
   std::stringstream ss;
   ss << t;
   return ss.str();