diff --git a/source/lib/win.h b/source/lib/win.h
index 8935be5c4f..77d9051a83 100755
--- a/source/lib/win.h
+++ b/source/lib/win.h
@@ -87,6 +87,7 @@ extern int aio_open_winhandle(HANDLE);
 #endif
 
 extern __declspec(dllimport) int __stdcall WSAStartup(WORD, void*);
+extern __declspec(dllimport) int __stdcall WSAGetLastError();
 #endif
 }