diff --git a/TODO.win32 b/TODO.win32
index 54162c82086..ff2daa1cad6 100644
--- a/TODO.win32
+++ b/TODO.win32
@@ -55,9 +55,6 @@
   If socket() fails it returns -1 so _open_osfhandle fails as well, but and we'll always return/throw EBADF.
   If _open_osfhandle fails but socket doesn't, a stray handle is left open. It should be fixed.
 
-- Check error number mappings.
-  Winsock errnos are sometimes different. Subtracting WSABASEERR from errnos works in most cases.
-
 - Think about `make install`
 
 - Extensions
diff --git a/lib/net.js b/lib/net.js
index 6eed683b9b2..efaf8165a9b 100644
--- a/lib/net.js
+++ b/lib/net.js
@@ -48,7 +48,7 @@ var errnoException = binding.errnoException;
 var sendMsg = binding.sendMsg;
 var recvMsg = binding.recvMsg;
 
-var EINPROGRESS = constants.EINPROGRESS;
+var EINPROGRESS = constants.EINPROGRESS || constants.WSAEINPROGRESS;
 var ENOENT = constants.ENOENT;
 var EMFILE = constants.EMFILE;
 
diff --git a/src/node.cc b/src/node.cc
index 5faa313c783..ab77db8f7a3 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -616,6 +616,234 @@ static inline const char *errno_string(int errorno) {
   ERRNO_CASE(EXDEV);
 #endif
 
+#ifdef WSAEINTR
+  ERRNO_CASE(WSAEINTR);
+#endif
+
+#ifdef WSAEBADF
+  ERRNO_CASE(WSAEBADF);
+#endif
+
+#ifdef WSAEACCES
+  ERRNO_CASE(WSAEACCES);
+#endif
+
+#ifdef WSAEFAULT
+  ERRNO_CASE(WSAEFAULT);
+#endif
+
+#ifdef WSAEINVAL
+  ERRNO_CASE(WSAEINVAL);
+#endif
+
+#ifdef WSAEMFILE
+  ERRNO_CASE(WSAEMFILE);
+#endif
+
+#ifdef WSAEWOULDBLOCK
+  ERRNO_CASE(WSAEWOULDBLOCK);
+#endif
+
+#ifdef WSAEINPROGRESS
+  ERRNO_CASE(WSAEINPROGRESS);
+#endif
+
+#ifdef WSAEALREADY
+  ERRNO_CASE(WSAEALREADY);
+#endif
+
+#ifdef WSAENOTSOCK
+  ERRNO_CASE(WSAENOTSOCK);
+#endif
+
+#ifdef WSAEDESTADDRREQ
+  ERRNO_CASE(WSAEDESTADDRREQ);
+#endif
+
+#ifdef WSAEMSGSIZE
+  ERRNO_CASE(WSAEMSGSIZE);
+#endif
+
+#ifdef WSAEPROTOTYPE
+  ERRNO_CASE(WSAEPROTOTYPE);
+#endif
+
+#ifdef WSAENOPROTOOPT
+  ERRNO_CASE(WSAENOPROTOOPT);
+#endif
+
+#ifdef WSAEPROTONOSUPPORT
+  ERRNO_CASE(WSAEPROTONOSUPPORT);
+#endif
+
+#ifdef WSAESOCKTNOSUPPORT
+  ERRNO_CASE(WSAESOCKTNOSUPPORT);
+#endif
+
+#ifdef WSAEOPNOTSUPP
+  ERRNO_CASE(WSAEOPNOTSUPP);
+#endif
+
+#ifdef WSAEPFNOSUPPORT
+  ERRNO_CASE(WSAEPFNOSUPPORT);
+#endif
+
+#ifdef WSAEAFNOSUPPORT
+  ERRNO_CASE(WSAEAFNOSUPPORT);
+#endif
+
+#ifdef WSAEADDRINUSE
+  ERRNO_CASE(WSAEADDRINUSE);
+#endif
+
+#ifdef WSAEADDRNOTAVAIL
+  ERRNO_CASE(WSAEADDRNOTAVAIL);
+#endif
+
+#ifdef WSAENETDOWN
+  ERRNO_CASE(WSAENETDOWN);
+#endif
+
+#ifdef WSAENETUNREACH
+  ERRNO_CASE(WSAENETUNREACH);
+#endif
+
+#ifdef WSAENETRESET
+  ERRNO_CASE(WSAENETRESET);
+#endif
+
+#ifdef WSAECONNABORTED
+  ERRNO_CASE(WSAECONNABORTED);
+#endif
+
+#ifdef WSAECONNRESET
+  ERRNO_CASE(WSAECONNRESET);
+#endif
+
+#ifdef WSAENOBUFS
+  ERRNO_CASE(WSAENOBUFS);
+#endif
+
+#ifdef WSAEISCONN
+  ERRNO_CASE(WSAEISCONN);
+#endif
+
+#ifdef WSAENOTCONN
+  ERRNO_CASE(WSAENOTCONN);
+#endif
+
+#ifdef WSAESHUTDOWN
+  ERRNO_CASE(WSAESHUTDOWN);
+#endif
+
+#ifdef WSAETOOMANYREFS
+  ERRNO_CASE(WSAETOOMANYREFS);
+#endif
+
+#ifdef WSAETIMEDOUT
+  ERRNO_CASE(WSAETIMEDOUT);
+#endif
+
+#ifdef WSAECONNREFUSED
+  ERRNO_CASE(WSAECONNREFUSED);
+#endif
+
+#ifdef WSAELOOP
+  ERRNO_CASE(WSAELOOP);
+#endif
+
+#ifdef WSAENAMETOOLONG
+  ERRNO_CASE(WSAENAMETOOLONG);
+#endif
+
+#ifdef WSAEHOSTDOWN
+  ERRNO_CASE(WSAEHOSTDOWN);
+#endif
+
+#ifdef WSAEHOSTUNREACH
+  ERRNO_CASE(WSAEHOSTUNREACH);
+#endif
+
+#ifdef WSAENOTEMPTY
+  ERRNO_CASE(WSAENOTEMPTY);
+#endif
+
+#ifdef WSAEPROCLIM
+  ERRNO_CASE(WSAEPROCLIM);
+#endif
+
+#ifdef WSAEUSERS
+  ERRNO_CASE(WSAEUSERS);
+#endif
+
+#ifdef WSAEDQUOT
+  ERRNO_CASE(WSAEDQUOT);
+#endif
+
+#ifdef WSAESTALE
+  ERRNO_CASE(WSAESTALE);
+#endif
+
+#ifdef WSAEREMOTE
+  ERRNO_CASE(WSAEREMOTE);
+#endif
+
+#ifdef WSASYSNOTREADY
+  ERRNO_CASE(WSASYSNOTREADY);
+#endif
+
+#ifdef WSAVERNOTSUPPORTED
+  ERRNO_CASE(WSAVERNOTSUPPORTED);
+#endif
+
+#ifdef WSANOTINITIALISED
+  ERRNO_CASE(WSANOTINITIALISED);
+#endif
+
+#ifdef WSAEDISCON
+  ERRNO_CASE(WSAEDISCON);
+#endif
+
+#ifdef WSAENOMORE
+  ERRNO_CASE(WSAENOMORE);
+#endif
+
+#ifdef WSAECANCELLED
+  ERRNO_CASE(WSAECANCELLED);
+#endif
+
+#ifdef WSAEINVALIDPROCTABLE
+  ERRNO_CASE(WSAEINVALIDPROCTABLE);
+#endif
+
+#ifdef WSAEINVALIDPROVIDER
+  ERRNO_CASE(WSAEINVALIDPROVIDER);
+#endif
+
+#ifdef WSAEPROVIDERFAILEDINIT
+  ERRNO_CASE(WSAEPROVIDERFAILEDINIT);
+#endif
+
+#ifdef WSASYSCALLFAILURE
+  ERRNO_CASE(WSASYSCALLFAILURE);
+#endif
+
+#ifdef WSASERVICE_NOT_FOUND
+  ERRNO_CASE(WSASERVICE_NOT_FOUND);
+#endif
+
+#ifdef WSATYPE_NOT_FOUND
+  ERRNO_CASE(WSATYPE_NOT_FOUND);
+#endif
+
+#ifdef WSA_E_NO_MORE
+  ERRNO_CASE(WSA_E_NO_MORE);
+#endif
+
+#ifdef WSA_E_CANCELLED
+  ERRNO_CASE(WSA_E_CANCELLED);
+#endif
+
   default: return "";
   }
 }
diff --git a/src/node_constants.cc b/src/node_constants.cc
index d82bca855f7..7ea372223eb 100644
--- a/src/node_constants.cc
+++ b/src/node_constants.cc
@@ -10,6 +10,11 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
+#ifdef __MINGW32__
+# include <platform_win32.h>
+# include <platform_win32_winsock.h>
+#endif
+
 namespace node {
 
 using namespace v8;
@@ -443,6 +448,238 @@ void DefineConstants(Handle<Object> target) {
   NODE_DEFINE_CONSTANT(target, EXDEV);
 #endif
 
+#ifdef WSAEINTR
+  NODE_DEFINE_CONSTANT(target, WSAEINTR);
+#endif
+
+#ifdef WSAEBADF
+  NODE_DEFINE_CONSTANT(target, WSAEBADF);
+#endif
+
+#ifdef WSAEACCES
+  NODE_DEFINE_CONSTANT(target, WSAEACCES);
+#endif
+
+#ifdef WSAEFAULT
+  NODE_DEFINE_CONSTANT(target, WSAEFAULT);
+#endif
+
+#ifdef WSAEINVAL
+  NODE_DEFINE_CONSTANT(target, WSAEINVAL);
+#endif
+
+#ifdef WSAEMFILE
+  NODE_DEFINE_CONSTANT(target, WSAEMFILE);
+#endif
+
+#ifdef WSAEWOULDBLOCK
+  NODE_DEFINE_CONSTANT(target, WSAEWOULDBLOCK);
+#endif
+
+#ifdef WSAEINPROGRESS
+  NODE_DEFINE_CONSTANT(target, WSAEINPROGRESS);
+#endif
+
+#ifdef WSAEALREADY
+  NODE_DEFINE_CONSTANT(target, WSAEALREADY);
+#endif
+
+#ifdef WSAENOTSOCK
+  NODE_DEFINE_CONSTANT(target, WSAENOTSOCK);
+#endif
+
+#ifdef WSAEDESTADDRREQ
+  NODE_DEFINE_CONSTANT(target, WSAEDESTADDRREQ);
+#endif
+
+#ifdef WSAEMSGSIZE
+  NODE_DEFINE_CONSTANT(target, WSAEMSGSIZE);
+#endif
+
+#ifdef WSAEPROTOTYPE
+  NODE_DEFINE_CONSTANT(target, WSAEPROTOTYPE);
+#endif
+
+#ifdef WSAENOPROTOOPT
+  NODE_DEFINE_CONSTANT(target, WSAENOPROTOOPT);
+#endif
+
+#ifdef WSAEPROTONOSUPPORT
+  NODE_DEFINE_CONSTANT(target, WSAEPROTONOSUPPORT);
+#endif
+
+#ifdef WSAESOCKTNOSUPPORT
+  NODE_DEFINE_CONSTANT(target, WSAESOCKTNOSUPPORT);
+#endif
+
+#ifdef WSAEOPNOTSUPP
+  NODE_DEFINE_CONSTANT(target, WSAEOPNOTSUPP);
+#endif
+
+#ifdef WSAEPFNOSUPPORT
+  NODE_DEFINE_CONSTANT(target, WSAEPFNOSUPPORT);
+#endif
+
+#ifdef WSAEAFNOSUPPORT
+  NODE_DEFINE_CONSTANT(target, WSAEAFNOSUPPORT);
+#endif
+
+#ifdef WSAEADDRINUSE
+  NODE_DEFINE_CONSTANT(target, WSAEADDRINUSE);
+#endif
+
+#ifdef WSAEADDRNOTAVAIL
+  NODE_DEFINE_CONSTANT(target, WSAEADDRNOTAVAIL);
+#endif
+
+#ifdef WSAENETDOWN
+  NODE_DEFINE_CONSTANT(target, WSAENETDOWN);
+#endif
+
+#ifdef WSAENETUNREACH
+  NODE_DEFINE_CONSTANT(target, WSAENETUNREACH);
+#endif
+
+#ifdef WSAENETRESET
+  NODE_DEFINE_CONSTANT(target, WSAENETRESET);
+#endif
+
+#ifdef WSAECONNABORTED
+  NODE_DEFINE_CONSTANT(target, WSAECONNABORTED);
+#endif
+
+#ifdef WSAECONNRESET
+  NODE_DEFINE_CONSTANT(target, WSAECONNRESET);
+#endif
+
+#ifdef WSAENOBUFS
+  NODE_DEFINE_CONSTANT(target, WSAENOBUFS);
+#endif
+
+#ifdef WSAEISCONN
+  NODE_DEFINE_CONSTANT(target, WSAEISCONN);
+#endif
+
+#ifdef WSAENOTCONN
+  NODE_DEFINE_CONSTANT(target, WSAENOTCONN);
+#endif
+
+#ifdef WSAESHUTDOWN
+  NODE_DEFINE_CONSTANT(target, WSAESHUTDOWN);
+#endif
+
+#ifdef WSAETOOMANYREFS
+  NODE_DEFINE_CONSTANT(target, WSAETOOMANYREFS);
+#endif
+
+#ifdef WSAETIMEDOUT
+  NODE_DEFINE_CONSTANT(target, WSAETIMEDOUT);
+#endif
+
+#ifdef WSAECONNREFUSED
+  NODE_DEFINE_CONSTANT(target, WSAECONNREFUSED);
+#endif
+
+#ifdef WSAELOOP
+  NODE_DEFINE_CONSTANT(target, WSAELOOP);
+#endif
+
+#ifdef WSAENAMETOOLONG
+  NODE_DEFINE_CONSTANT(target, WSAENAMETOOLONG);
+#endif
+
+#ifdef WSAEHOSTDOWN
+  NODE_DEFINE_CONSTANT(target, WSAEHOSTDOWN);
+#endif
+
+#ifdef WSAEHOSTUNREACH
+  NODE_DEFINE_CONSTANT(target, WSAEHOSTUNREACH);
+#endif
+
+#ifdef WSAENOTEMPTY
+  NODE_DEFINE_CONSTANT(target, WSAENOTEMPTY);
+#endif
+
+#ifdef WSAEPROCLIM
+  NODE_DEFINE_CONSTANT(target, WSAEPROCLIM);
+#endif
+
+#ifdef WSAEUSERS
+  NODE_DEFINE_CONSTANT(target, WSAEUSERS);
+#endif
+
+#ifdef WSAEDQUOT
+  NODE_DEFINE_CONSTANT(target, WSAEDQUOT);
+#endif
+
+#ifdef WSAESTALE
+  NODE_DEFINE_CONSTANT(target, WSAESTALE);
+#endif
+
+#ifdef WSAEREMOTE
+  NODE_DEFINE_CONSTANT(target, WSAEREMOTE);
+#endif
+
+#ifdef WSASYSNOTREADY
+  NODE_DEFINE_CONSTANT(target, WSASYSNOTREADY);
+#endif
+
+#ifdef WSAVERNOTSUPPORTED
+  NODE_DEFINE_CONSTANT(target, WSAVERNOTSUPPORTED);
+#endif
+
+#ifdef WSANOTINITIALISED
+  NODE_DEFINE_CONSTANT(target, WSANOTINITIALISED);
+#endif
+
+#ifdef WSAEDISCON
+  NODE_DEFINE_CONSTANT(target, WSAEDISCON);
+#endif
+
+#ifdef WSAENOMORE
+  NODE_DEFINE_CONSTANT(target, WSAENOMORE);
+#endif
+
+#ifdef WSAECANCELLED
+  NODE_DEFINE_CONSTANT(target, WSAECANCELLED);
+#endif
+
+#ifdef WSAEINVALIDPROCTABLE
+  NODE_DEFINE_CONSTANT(target, WSAEINVALIDPROCTABLE);
+#endif
+
+#ifdef WSAEINVALIDPROVIDER
+  NODE_DEFINE_CONSTANT(target, WSAEINVALIDPROVIDER);
+#endif
+
+#ifdef WSAEPROVIDERFAILEDINIT
+  NODE_DEFINE_CONSTANT(target, WSAEPROVIDERFAILEDINIT);
+#endif
+
+#ifdef WSASYSCALLFAILURE
+  NODE_DEFINE_CONSTANT(target, WSASYSCALLFAILURE);
+#endif
+
+#ifdef WSASERVICE_NOT_FOUND
+  NODE_DEFINE_CONSTANT(target, WSASERVICE_NOT_FOUND);
+#endif
+
+#ifdef WSATYPE_NOT_FOUND
+  NODE_DEFINE_CONSTANT(target, WSATYPE_NOT_FOUND);
+#endif
+
+#ifdef WSA_E_NO_MORE
+  NODE_DEFINE_CONSTANT(target, WSA_E_NO_MORE);
+#endif
+
+#ifdef WSA_E_CANCELLED
+  NODE_DEFINE_CONSTANT(target, WSA_E_CANCELLED);
+#endif
+
+#ifdef WSAEREFUSED
+  NODE_DEFINE_CONSTANT(target, WSAEREFUSED);
+#endif
+
 #ifdef SIGHUP
   NODE_DEFINE_CONSTANT(target, SIGHUP);
 #endif
diff --git a/src/node_os.cc b/src/node_os.cc
index b5b97af6e97..8c85d1b0c8f 100644
--- a/src/node_os.cc
+++ b/src/node_os.cc
@@ -28,10 +28,11 @@ static Handle<Value> GetHostname(const Arguments& args) {
   int r = gethostname(s, 255);
 
   if (r < 0) {
-#ifdef __MINGW32__
-    errno = WSAGetLastError() - WSABASEERR;
-#endif
+#ifdef __POSIX__
     return ThrowException(ErrnoException(errno, "gethostname"));
+#else // __MINGW32__
+    return ThrowException(ErrnoException(WSAGetLastError(), "gethostname"));
+#endif // __MINGW32__
   }
 
   return scope.Close(String::New(s));