diff --git a/CMakeLists.txt b/CMakeLists.txt
index d7006c6..742ebf7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,7 +4,7 @@ project(gsplus VERSION 0.14)
 
 if(CYGWIN OR MSYS)
 	set(WIN32 1)
-	add_definitions(-DWIN32 -D_WIN32)
+	add_definitions(-DWIN32 -D_WIN32 -D__USE_W32_SOCKETS)
 endif()
 
 # msys/cygwin/mingw32 add dirent.h, etc.
@@ -20,4 +20,4 @@ if(WIN32)
 	include_directories(include/npcap)
 endif()
 
-add_subdirectory(src bin)
\ No newline at end of file
+add_subdirectory(src bin)