diff -r -u boost_1_61_0-1/boost/system/api_config.hpp boost_1_61_0-2/boost/system/api_config.hpp
--- boost_1_61_0-1/boost/system/api_config.hpp	2015-01-06 17:08:27.000000000 +0100
+++ boost_1_61_0-2/boost/system/api_config.hpp	2015-09-07 13:07:21.479569725 +0200
@@ -33,7 +33,7 @@
 //    Standalone MinGW and all other known Windows compilers do predefine _WIN32
 //    Compilers that predefine _WIN32 or __MINGW32__ do so for Windows 64-bit builds too.
 
-# if defined(_WIN32) || defined(__CYGWIN__) // Windows default, including MinGW and Cygwin
+# if defined(_WIN32) // Windows default, including MinGW
 #   define BOOST_WINDOWS_API
 # else
 #   define BOOST_POSIX_API