diff --git a/config/ac_func_accept_argtypes.m4 b/config/ac_func_accept_argtypes.m4
index 1e7717922d..a82788dd97 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 ebe69cdb38..67c5632139 100755
--- a/configure
+++ b/configure
@@ -14328,6 +14328,159 @@ done
 
 fi
 
+if test "$PORTNAME" = "win32" ; then
+
+for ac_header in crtdefs.h
+do
+as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
+if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
+  { $as_echo "$as_me:$LINENO: checking for $ac_header" >&5
+$as_echo_n "checking for $ac_header... " >&6; }
+if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
+  $as_echo_n "(cached) " >&6
+fi
+ac_res=`eval 'as_val=${'$as_ac_Header'}
+		 $as_echo "$as_val"'`
+	       { $as_echo "$as_me:$LINENO: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+else
+  # Is the header compilable?
+{ $as_echo "$as_me:$LINENO: checking $ac_header usability" >&5
+$as_echo_n "checking $ac_header usability... " >&6; }
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+$ac_includes_default
+#include <$ac_header>
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  ac_header_compiler=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	ac_header_compiler=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+{ $as_echo "$as_me:$LINENO: result: $ac_header_compiler" >&5
+$as_echo "$ac_header_compiler" >&6; }
+
+# Is the header present?
+{ $as_echo "$as_me:$LINENO: checking $ac_header presence" >&5
+$as_echo_n "checking $ac_header presence... " >&6; }
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <$ac_header>
+_ACEOF
+if { (ac_try="$ac_cpp conftest.$ac_ext"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_cpp conftest.$ac_ext") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } >/dev/null && {
+	 test -z "$ac_c_preproc_warn_flag$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       }; then
+  ac_header_preproc=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+  ac_header_preproc=no
+fi
+
+rm -f conftest.err conftest.$ac_ext
+{ $as_echo "$as_me:$LINENO: result: $ac_header_preproc" >&5
+$as_echo "$ac_header_preproc" >&6; }
+
+# So?  What about this header?
+case $ac_header_compiler:$ac_header_preproc:$ac_c_preproc_warn_flag in
+  yes:no: )
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header: accepted by the compiler, rejected by the preprocessor!" >&5
+$as_echo "$as_me: WARNING: $ac_header: accepted by the compiler, rejected by the preprocessor!" >&2;}
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header: proceeding with the compiler's result" >&5
+$as_echo "$as_me: WARNING: $ac_header: proceeding with the compiler's result" >&2;}
+    ac_header_preproc=yes
+    ;;
+  no:yes:* )
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header: present but cannot be compiled" >&5
+$as_echo "$as_me: WARNING: $ac_header: present but cannot be compiled" >&2;}
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header:     check for missing prerequisite headers?" >&5
+$as_echo "$as_me: WARNING: $ac_header:     check for missing prerequisite headers?" >&2;}
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header: see the Autoconf documentation" >&5
+$as_echo "$as_me: WARNING: $ac_header: see the Autoconf documentation" >&2;}
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header:     section \"Present But Cannot Be Compiled\"" >&5
+$as_echo "$as_me: WARNING: $ac_header:     section \"Present But Cannot Be Compiled\"" >&2;}
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header: proceeding with the preprocessor's result" >&5
+$as_echo "$as_me: WARNING: $ac_header: proceeding with the preprocessor's result" >&2;}
+    { $as_echo "$as_me:$LINENO: WARNING: $ac_header: in the future, the compiler will take precedence" >&5
+$as_echo "$as_me: WARNING: $ac_header: in the future, the compiler will take precedence" >&2;}
+    ( cat <<\_ASBOX
+## ---------------------------------------- ##
+## Report this to pgsql-bugs@postgresql.org ##
+## ---------------------------------------- ##
+_ASBOX
+     ) | sed "s/^/$as_me: WARNING:     /" >&2
+    ;;
+esac
+{ $as_echo "$as_me:$LINENO: checking for $ac_header" >&5
+$as_echo_n "checking for $ac_header... " >&6; }
+if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
+  $as_echo_n "(cached) " >&6
+else
+  eval "$as_ac_Header=\$ac_header_preproc"
+fi
+ac_res=`eval 'as_val=${'$as_ac_Header'}
+		 $as_echo "$as_val"'`
+	       { $as_echo "$as_me:$LINENO: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+
+fi
+as_val=`eval 'as_val=${'$as_ac_Header'}
+		 $as_echo "$as_val"'`
+   if test "x$as_val" = x""yes; then
+  cat >>confdefs.h <<_ACEOF
+#define `$as_echo "HAVE_$ac_header" | $as_tr_cpp` 1
+_ACEOF
+
+fi
+
+done
+
+fi
 
 ##
 ## Types, structures, compiler characteristics
@@ -17997,7 +18150,8 @@ 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.
-# Check whether --enable-largefile was given.
+if test "$PORTNAME" != "win32"; then
+   # Check whether --enable-largefile was given.
 if test "${enable_largefile+set}" = set; then
   enableval=$enable_largefile;
 fi
@@ -18353,6 +18507,7 @@ 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
@@ -18808,7 +18963,7 @@ else
      if test "${ac_cv_func_accept_arg3+set}" = set; then
   $as_echo_n "(cached) " >&6
 else
-      for ac_cv_func_accept_return in 'int' 'unsigned int PASCAL' 'SOCKET'; do
+      for ac_cv_func_accept_return in 'int' 'unsigned int PASCAL' 'SOCKET WSAAPI'; do
       for ac_cv_func_accept_arg1 in 'int' 'unsigned int' 'SOCKET'; do
        for ac_cv_func_accept_arg2 in 'struct sockaddr *' 'const struct sockaddr *' 'void *'; do
         for ac_cv_func_accept_arg3 in 'int' 'size_t' 'socklen_t' 'unsigned int' 'void'; do
diff --git a/configure.in b/configure.in
index 5591b93e75..9cf084d4b6 100644
--- a/configure.in
+++ b/configure.in
@@ -1101,6 +1101,9 @@ if test "$with_ossp_uuid" = yes ; then
       [AC_MSG_ERROR([header file <ossp/uuid.h> or <uuid.h> is required for OSSP-UUID])])])
 fi
 
+if test "$PORTNAME" = "win32" ; then
+   AC_CHECK_HEADERS(crtdefs.h)
+fi
 
 ##
 ## Types, structures, compiler characteristics
@@ -1174,7 +1177,9 @@ 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.
-AC_SYS_LARGEFILE
+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 0391860846..cb9b150f8a 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -58,7 +58,8 @@
 #endif
 #include "postgres_ext.h"
 
-#if _MSC_VER >= 1400 || defined(WIN64)
+#define HAVE_CRTDEFS_H 1
+#if _MSC_VER >= 1400 || defined(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 15fe0bfff4..b969d8c8e6 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 34f4004129..afc96283eb 100644
--- a/src/include/port/win32.h
+++ b/src/include/port/win32.h
@@ -31,7 +31,7 @@
  * The Mingw64 headers choke if this is already defined - they
  * define it themselves.
  */
-#if !defined(WIN64) || defined(WIN32_ONLY_COMPILER)
+#if !defined(__MINGW64_VERSION_MAJOR) || defined(WIN32_ONLY_COMPILER)
 #define _WINSOCKAPI_
 #endif
 #include <winsock2.h>
@@ -225,9 +225,13 @@ 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 +268,36 @@ 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/ecpg/test/resultmap b/src/interfaces/ecpg/test/resultmap
index 95ea5831cc..aef7338e81 100644
--- a/src/interfaces/ecpg/test/resultmap
+++ b/src/interfaces/ecpg/test/resultmap
@@ -1,9 +1,12 @@
 compat_informix/dec_test:stdout:i.86-pc-win32vc=compat_informix-dec_test-MinGW32.stdout
 compat_informix/dec_test:stdout:i.86-pc-mingw32=compat_informix-dec_test-MinGW32.stdout
 compat_informix/dec_test:stdout:x86_64-w64-mingw32=compat_informix-dec_test-MinGW32.stdout
+compat_informix/dec_test:stdout:i.86-w64-mingw32=compat_informix-dec_test-MinGW32.stdout
 pgtypeslib/num_test:stdout:i.86-pc-win32vc=pgtypeslib-num_test-MinGW32.stdout
 pgtypeslib/num_test:stdout:i.86-pc-mingw32=pgtypeslib-num_test-MinGW32.stdout
 pgtypeslib/num_test:stdout:x86_64-w64-mingw32=pgtypeslib-num_test-MinGW32.stdout
+pgtypeslib/num_test:stdout:i.86-w64-mingw32=pgtypeslib-num_test-MinGW32.stdout
 pgtypeslib/num_test2:stdout:i.86-pc-win32vc=pgtypeslib-num_test2-MinGW32.stdout
 pgtypeslib/num_test2:stdout:i.86-pc-mingw32=pgtypeslib-num_test2-MinGW32.stdout
 pgtypeslib/num_test2:stdout:x86_64-w64-mingw32=pgtypeslib-num_test2-MinGW32.stdout
+pgtypeslib/num_test2:stdout:i.86-w64-mingw32=pgtypeslib-num_test2-MinGW32.stdout
diff --git a/src/interfaces/libpq/win32.h b/src/interfaces/libpq/win32.h
index b65da9ada1..be00ea73cb 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 db19878ae1..b6368ae691 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";
diff --git a/src/test/regress/resultmap b/src/test/regress/resultmap
index d02d221d56..04ba99fe33 100644
--- a/src/test/regress/resultmap
+++ b/src/test/regress/resultmap
@@ -1,5 +1,6 @@
 float4:out:i.86-pc-mingw32=float4-exp-three-digits.out
 float4:out:x86_64-w64-mingw32=float4-exp-three-digits.out
+float4:out:i.86-w64-mingw32=float4-exp-three-digits.out
 float4:out:i.86-pc-win32vc=float4-exp-three-digits.out
 float8:out:i.86-.*-freebsd=float8-small-is-zero.out
 float8:out:i.86-.*-openbsd=float8-small-is-zero.out
@@ -7,8 +8,10 @@ float8:out:i.86-.*-netbsd=float8-small-is-zero.out
 float8:out:m68k-.*-netbsd=float8-small-is-zero.out
 float8:out:i.86-pc-mingw32=float8-exp-three-digits-win32.out
 float8:out:x86_64-w64-mingw32=float8-exp-three-digits-win32.out
+float8:out:i.86-w64-mingw32=float8-exp-three-digits-win32.out
 float8:out:i.86-pc-win32vc=float8-exp-three-digits-win32.out
 float8:out:i.86-pc-cygwin=float8-small-is-zero.out
 int8:out:i.86-pc-mingw32=int8-exp-three-digits.out
 int8:out:x86_64-w64-mingw32=int8-exp-three-digits.out
+int8:out:i.86-w64-mingw32=int8-exp-three-digits.out
 int8:out:i.86-pc-win32vc=int8-exp-three-digits.out