diff --git a/config/ac_func_accept_argtypes.m4 b/config/ac_func_accept_argtypes.m4
index 1e77179..a82788d 100644
--- a/config/ac_func_accept_argtypes.m4
+++ b/config/ac_func_accept_argtypes.m4
@@ -46,7 +46,7 @@ AC_DEFUN([AC_FUNC_ACCEPT_ARGTYPES],
  [AC_CACHE_VAL(ac_cv_func_accept_arg1,dnl
   [AC_CACHE_VAL(ac_cv_func_accept_arg2,dnl
    [AC_CACHE_VAL(ac_cv_func_accept_arg3,dnl
-    [for ac_cv_func_accept_return in 'int' 'unsigned int PASCAL' 'SOCKET'; do
+    [for ac_cv_func_accept_return in 'int' 'unsigned int PASCAL' 'SOCKET WSAAPI'; do
       for ac_cv_func_accept_arg1 in 'int' 'unsigned int' 'SOCKET'; do
        for ac_cv_func_accept_arg2 in 'struct sockaddr *' 'const struct sockaddr *' 'void *'; do
         for ac_cv_func_accept_arg3 in 'int' 'size_t' 'socklen_t' 'unsigned int' 'void'; do
diff --git a/configure b/configure
index de9ba5a..dfdd034 100755
--- a/configure
+++ b/configure
@@ -10056,7 +10056,8 @@ done
 
 
 
-for ac_header in crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/ucred.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h kernel/OS.h kernel/image.h SupportDefs.h
+
+for ac_header in crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/ucred.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h kernel/OS.h kernel/image.h SupportDefs.h crtdefs.h
 do
 as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
@@ -17997,6 +17998,7 @@ fi
 # compiler characteristic, but you'd be wrong.  We must check this before
 # probing existence of related functions such as fseeko, since the largefile
 # defines can affect what is generated for that.
+if test "$PORTNAME" != "win32" ; then
 # Check whether --enable-largefile was given.
 if test "${enable_largefile+set}" = set; then
   enableval=$enable_largefile;
@@ -18353,7 +18355,7 @@ rm -rf conftest*
   fi
 fi
 
-
+fi
 # Check for largefile support (must be after AC_SYS_LARGEFILE)
 # The cast to long int works around a bug in the HP C Compiler
 # version HP92453-01 B.11.11.23709.GP, which incorrectly rejects
@@ -18808,7 +18810,7 @@ else
      if test "${ac_cv_func_accept_arg3+set}" = set; then
   $as_echo_n "(cached) " >&6
 else
-      for ac_cv_func_accept_return in 'int' 'unsigned int PASCAL' 'SOCKET'; do
+      for ac_cv_func_accept_return in 'int' 'unsigned int PASCAL' 'SOCKET WSAAPI'; do
       for ac_cv_func_accept_arg1 in 'int' 'unsigned int' 'SOCKET'; do
        for ac_cv_func_accept_arg2 in 'struct sockaddr *' 'const struct sockaddr *' 'void *'; do
         for ac_cv_func_accept_arg3 in 'int' 'size_t' 'socklen_t' 'unsigned int' 'void'; do
diff --git a/configure.in b/configure.in
index 5591b93..79180df 100644
--- a/configure.in
+++ b/configure.in
@@ -985,7 +985,7 @@ AC_SUBST(OSSP_UUID_LIBS)
 ##
 
 dnl sys/socket.h is required by AC_FUNC_ACCEPT_ARGTYPES
-AC_CHECK_HEADERS([crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/ucred.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h kernel/OS.h kernel/image.h SupportDefs.h])
+AC_CHECK_HEADERS([crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/ucred.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h kernel/OS.h kernel/image.h SupportDefs.h crtdefs.h])
 
 # On BSD, cpp test for net/if.h will fail unless sys/socket.h
 # is included first.
@@ -1174,8 +1174,9 @@ fi
 # compiler characteristic, but you'd be wrong.  We must check this before
 # probing existence of related functions such as fseeko, since the largefile
 # defines can affect what is generated for that.
+if test "$PORTNAME" != "win32" ; then
 AC_SYS_LARGEFILE
-
+fi
 # Check for largefile support (must be after AC_SYS_LARGEFILE)
 AC_CHECK_SIZEOF([off_t])
 
diff --git a/src/include/c.h b/src/include/c.h
index 0391860..14f6443 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -58,7 +58,7 @@
 #endif
 #include "postgres_ext.h"
 
-#if _MSC_VER >= 1400 || defined(WIN64)
+#if _MSC_VER >= 1400 || HAVE_CRTDEFS_H
 #define errcode __msvc_errcode
 #include <crtdefs.h>
 #undef errcode
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 15fe0bf..b969d8c 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -99,6 +99,9 @@
 /* Define to 1 if you have the `class' function. */
 #undef HAVE_CLASS
 
+/* Define to 1 if you have the <crtdefs.h> header file. */
+#undef HAVE_CRTDEFS_H
+
 /* Define to 1 if you have the `crypt' function. */
 #undef HAVE_CRYPT
 
diff --git a/src/include/port/win32.h b/src/include/port/win32.h
index 34f4004..ca9ae0c 100644
--- a/src/include/port/win32.h
+++ b/src/include/port/win32.h
@@ -27,13 +27,6 @@
 
 #undef ERROR
 
-/*
- * The Mingw64 headers choke if this is already defined - they
- * define it themselves.
- */
-#if !defined(WIN64) || defined(WIN32_ONLY_COMPILER)
-#define _WINSOCKAPI_
-#endif
 #include <winsock2.h>
 #include <ws2tcpip.h>
 #include <windows.h>
@@ -225,9 +218,13 @@ int			setitimer(int which, const struct itimerval * value, struct itimerval * ov
 #define fseeko(stream, offset, origin) _fseeki64(stream, offset, origin)
 #define ftello(stream) _ftelli64(stream)
 #else
+#ifndef fseeko
 #define fseeko(stream, offset, origin) fseeko64(stream, offset, origin)
+#endif
+#ifndef ftello
 #define ftello(stream) ftello64(stream)
 #endif
+#endif
 
 /*
  * Supplement to <sys/types.h>.
@@ -264,16 +261,37 @@ typedef int pid_t;
 #undef EINTR
 #define EINTR WSAEINTR
 #define EAGAIN WSAEWOULDBLOCK
+
+#ifndef EMSGSIZE
 #define EMSGSIZE WSAEMSGSIZE
+#endif
+#ifndef EAFNOSUPPORT
 #define EAFNOSUPPORT WSAEAFNOSUPPORT
+#endif
+#ifndef EWOULDBLOCK
 #define EWOULDBLOCK WSAEWOULDBLOCK
+#endif
+#ifndef ECONNRESET
 #define ECONNRESET WSAECONNRESET
+#endif
+#ifndef EINPROGRESS
 #define EINPROGRESS WSAEINPROGRESS
+#endif
+#ifndef ENOBUFS
 #define ENOBUFS WSAENOBUFS
+#endif
+#ifndef EPROTONOSUPPORT
 #define EPROTONOSUPPORT WSAEPROTONOSUPPORT
+#endif
+#ifndef ECONNREFUSED
 #define ECONNREFUSED WSAECONNREFUSED
+#endif
+#ifndef EBADFD
 #define EBADFD WSAENOTSOCK
+#endif
+#ifndef EOPNOTSUPP
 #define EOPNOTSUPP WSAEOPNOTSUPP
+#endif
 
 /*
  * Extended locale functions with gratuitous underscore prefixes.
diff --git a/src/interfaces/libpq/win32.h b/src/interfaces/libpq/win32.h
index b65da9a..be00ea7 100644
--- a/src/interfaces/libpq/win32.h
+++ b/src/interfaces/libpq/win32.h
@@ -22,9 +22,15 @@
 #undef EAGAIN					/* doesn't apply on sockets */
 #undef EINTR
 #define EINTR WSAEINTR
+#ifndef EWOULDBLOCK
 #define EWOULDBLOCK WSAEWOULDBLOCK
+#endif
+#ifndef ECONNRESET
 #define ECONNRESET WSAECONNRESET
+#endif
+#ifndef EINPROGRESS
 #define EINPROGRESS WSAEINPROGRESS
+#endif
 
 /*
  * support for handling Windows Socket errors
diff --git a/src/port/getaddrinfo.c b/src/port/getaddrinfo.c
index db19878..c2bed94 100644
--- a/src/port/getaddrinfo.c
+++ b/src/port/getaddrinfo.c
@@ -328,12 +328,10 @@ gai_strerror(int errcode)
 		case EAI_MEMORY:
 			return "Not enough memory";
 #endif
-#ifdef EAI_NODATA
-#if !defined(WIN64) && !defined(WIN32_ONLY_COMPILER)	/* MSVC/WIN64 duplicate */
+#if defined(EAI_NODATA) && EAI_NODATA != EAI_NONAME	/* MSVC/WIN64 duplicate */
 		case EAI_NODATA:
 			return "No host data of that type was found";
 #endif
-#endif
 #ifdef EAI_SERVICE
 		case EAI_SERVICE:
 			return "Class type not found";