diff --git a/lib/setup_once.h b/lib/setup_once.h
index 473eef2..f0a6110 100644
--- a/lib/setup_once.h
+++ b/lib/setup_once.h
@@ -373,41 +373,95 @@ typedef int sig_atomic_t;
 #define EINTR            WSAEINTR
 #undef  EINVAL           /* override definition in errno.h */
 #define EINVAL           WSAEINVAL
-#define EWOULDBLOCK      WSAEWOULDBLOCK
-#define EINPROGRESS      WSAEINPROGRESS
-#define EALREADY         WSAEALREADY
-#define ENOTSOCK         WSAENOTSOCK
-#define EDESTADDRREQ     WSAEDESTADDRREQ
-#define EMSGSIZE         WSAEMSGSIZE
-#define EPROTOTYPE       WSAEPROTOTYPE
-#define ENOPROTOOPT      WSAENOPROTOOPT
-#define EPROTONOSUPPORT  WSAEPROTONOSUPPORT
-#define ESOCKTNOSUPPORT  WSAESOCKTNOSUPPORT
-#define EOPNOTSUPP       WSAEOPNOTSUPP
-#define EPFNOSUPPORT     WSAEPFNOSUPPORT
-#define EAFNOSUPPORT     WSAEAFNOSUPPORT
-#define EADDRINUSE       WSAEADDRINUSE
-#define EADDRNOTAVAIL    WSAEADDRNOTAVAIL
-#define ENETDOWN         WSAENETDOWN
-#define ENETUNREACH      WSAENETUNREACH
-#define ENETRESET        WSAENETRESET
-#define ECONNABORTED     WSAECONNABORTED
-#define ECONNRESET       WSAECONNRESET
+#ifndef EWOULDBLOCK
+# define EWOULDBLOCK      WSAEWOULDBLOCK
+#endif
+#ifndef EINPROGRESS
+# define EINPROGRESS      WSAEINPROGRESS
+#endif
+#ifndef EALREADY
+# define EALREADY         WSAEALREADY
+#endif
+#ifndef ENOTSOCK
+# define ENOTSOCK         WSAENOTSOCK
+#endif
+#ifndef EDESTADDRREQ
+# define EDESTADDRREQ     WSAEDESTADDRREQ
+#endif
+#ifndef EMSGSIZE
+# define EMSGSIZE         WSAEMSGSIZE
+#endif
+#ifndef EPROTOTYPE
+# define EPROTOTYPE       WSAEPROTOTYPE
+#endif
+#ifndef ENOPROTOOPT
+# define ENOPROTOOPT      WSAENOPROTOOPT
+#endif
+#ifndef EPROTONOSUPPORT
+# define EPROTONOSUPPORT  WSAEPROTONOSUPPORT
+#endif
+#ifndef ESOCKTNOSUPPORT
+# define ESOCKTNOSUPPORT  WSAESOCKTNOSUPPORT
+#endif
+#ifndef EOPNOTSUPP
+# define EOPNOTSUPP       WSAEOPNOTSUPP
+#endif
+#ifndef EPFNOSUPPORT
+# define EPFNOSUPPORT     WSAEPFNOSUPPORT
+#endif
+#ifndef EAFNOSUPPORT
+# define EAFNOSUPPORT     WSAEAFNOSUPPORT
+#endif
+#ifndef EADDRINUSE
+# define EADDRINUSE       WSAEADDRINUSE
+#endif
+#ifndef EADDRNOTAVAIL
+# define EADDRNOTAVAIL    WSAEADDRNOTAVAIL
+#endif
+#ifndef ENETDOWN
+# define ENETDOWN         WSAENETDOWN
+#endif
+#ifndef ENETUNREACH
+# define ENETUNREACH      WSAENETUNREACH
+#endif
+#ifndef ENETRESET
+# define ENETRESET        WSAENETRESET
+#endif
+#ifndef ECONNABORTED
+# define ECONNABORTED     WSAECONNABORTED
+#endif
+#ifndef ECONNRESET
+# define ECONNRESET       WSAECONNRESET
+#endif
+#ifndef ENOBUFS
 #define ENOBUFS          WSAENOBUFS
-#define EISCONN          WSAEISCONN
+#endif
+#ifndef EISCONN
+# define EISCONN          WSAEISCONN
+#endif
+#ifndef ENOTCONN
 #define ENOTCONN         WSAENOTCONN
+#endif
 #define ESHUTDOWN        WSAESHUTDOWN
 #define ETOOMANYREFS     WSAETOOMANYREFS
-#define ETIMEDOUT        WSAETIMEDOUT
-#define ECONNREFUSED     WSAECONNREFUSED
-#define ELOOP            WSAELOOP
+#ifndef ETIMEDOUT
+# define ETIMEDOUT        WSAETIMEDOUT
+#endif
+#ifndef ECONNREFUSED
+# define ECONNREFUSED     WSAECONNREFUSED
+#endif
+#ifndef ELOOP
+# define ELOOP            WSAELOOP
+#endif
 #ifndef ENAMETOOLONG     /* possible previous definition in errno.h */
-#define ENAMETOOLONG     WSAENAMETOOLONG
+# define ENAMETOOLONG     WSAENAMETOOLONG
 #endif
 #define EHOSTDOWN        WSAEHOSTDOWN
-#define EHOSTUNREACH     WSAEHOSTUNREACH
+#ifndef ENAMETOOLONG
+# define EHOSTUNREACH     WSAEHOSTUNREACH
+#endif
 #ifndef ENOTEMPTY        /* possible previous definition in errno.h */
-#define ENOTEMPTY        WSAENOTEMPTY
+# define ENOTEMPTY        WSAENOTEMPTY
 #endif
 #define EPROCLIM         WSAEPROCLIM
 #define EUSERS           WSAEUSERS