diff --git a/otherlibs/win32unix/accept.c b/otherlibs/win32unix/accept.c
index f751c3e39..0e44f5800 100644
--- a/otherlibs/win32unix/accept.c
+++ b/otherlibs/win32unix/accept.c
@@ -29,7 +29,7 @@ CAMLprim value unix_accept(sock)
   int oldvalue, oldvaluelen, newvalue, retcode;
   union sock_addr_union addr;
   socklen_param_type addr_len;
-  int errcode = 0;
+  DWORD errcode = 0;
 
   oldvaluelen = sizeof(oldvalue);
   retcode = getsockopt(INVALID_SOCKET, SOL_SOCKET, SO_OPENTYPE,
@@ -43,9 +43,8 @@ CAMLprim value unix_accept(sock)
   addr_len = sizeof(sock_addr);
   enter_blocking_section();
   snew = accept(sconn, &addr.s_gen, &addr_len);
+  if (snew == INVALID_SOCKET) errcode = WSAGetLastError ();
   leave_blocking_section();
-  if( snew == INVALID_SOCKET )
-    errcode = WSAGetLastError ();
   if (retcode == 0) {
     /* Restore initial mode */
     setsockopt(INVALID_SOCKET, SOL_SOCKET, SO_OPENTYPE, 
diff --git a/otherlibs/win32unix/connect.c b/otherlibs/win32unix/connect.c
index 74e62252d..da7d09c71 100644
--- a/otherlibs/win32unix/connect.c
+++ b/otherlibs/win32unix/connect.c
@@ -22,16 +22,17 @@ CAMLprim value unix_connect(socket, address)
      value socket, address;
 {
   SOCKET s = Socket_val(socket);
-  int retcode;
   union sock_addr_union addr;
   socklen_param_type addr_len;
+  DWORD errcode = 0;
 
   get_sockaddr(address, &addr, &addr_len);
   enter_blocking_section();
-  retcode = connect(s, &addr.s_gen, addr_len);
+  if (connect(s, &addr.s_gen, addr_len) == -1)
+    errcode = WSAGetLastError();
   leave_blocking_section();
-  if (retcode == -1) {
-    win32_maperr(WSAGetLastError());
+  if (errcode) {
+    win32_maperr(errcode);
     uerror("connect", Nothing);
   }
   return Val_unit;
diff --git a/otherlibs/win32unix/read.c b/otherlibs/win32unix/read.c
index 704cec2c7..c87d55ed0 100644
--- a/otherlibs/win32unix/read.c
+++ b/otherlibs/win32unix/read.c
@@ -19,35 +19,34 @@
 #include <signals.h>
 #include "unixsupport.h"
 
-CAMLprim value unix_read(value fd, value buf, value ofs, value len)
+CAMLprim value unix_read(value fd, value buf, value ofs, value vlen)
 {
+  intnat len;
   DWORD numbytes, numread;
   char iobuf[UNIX_BUFFER_SIZE];
+  DOWRD errcode = 0;
 
   Begin_root (buf);
-    numbytes = Long_val(len);
-    if (numbytes > UNIX_BUFFER_SIZE) numbytes = UNIX_BUFFER_SIZE;
+    len = Long_val(vlen);
+    numbytes = len > UNIX_BUFFER_SIZE ? UNIX_BUFFER_SIZE : len;
     if (Descr_kind_val(fd) == KIND_SOCKET) {
       int ret;
       SOCKET s = Socket_val(fd);
       enter_blocking_section();
       ret = recv(s, iobuf, numbytes, 0);
+      if (ret == SOCKET_ERROR) errcode = WSAGetLastError();
       leave_blocking_section();
-      if (ret == SOCKET_ERROR) {
-        win32_maperr(WSAGetLastError());
-        uerror("read", Nothing);
-      }
       numread = ret;
     } else {
-      BOOL ret;
       HANDLE h = Handle_val(fd);
       enter_blocking_section();
-      ret = ReadFile(h, iobuf, numbytes, &numread, NULL);
+      if (! ReadFile(h, iobuf, numbytes, &numread, NULL))
+        errcode = GetLastError();
       leave_blocking_section();
-      if (! ret) {
-        win32_maperr(GetLastError());
-        uerror("read", Nothing);
-      }
+    }
+    if (errcode) {
+      win32_maperr(errcode);
+      uerror("read", Nothing);
     }
     memmove (&Byte(buf, Long_val(ofs)), iobuf, numread);
   End_roots();
diff --git a/otherlibs/win32unix/select.c b/otherlibs/win32unix/select.c
index 4fa8e788b..a7b68217e 100644
--- a/otherlibs/win32unix/select.c
+++ b/otherlibs/win32unix/select.c
@@ -54,6 +54,7 @@ CAMLprim value unix_select(value readfds, value writefds, value exceptfds, value
   int retcode;
   value res;
   value read_list = Val_unit, write_list = Val_unit, except_list = Val_unit;
+  DWORD errcode = 0;
 
   Begin_roots3 (readfds, writefds, exceptfds)
   Begin_roots3 (read_list, write_list, except_list)
@@ -79,10 +80,11 @@ CAMLprim value unix_select(value readfds, value writefds, value exceptfds, value
 	tvp = &tv;
       }
       enter_blocking_section();
-      retcode = select(FD_SETSIZE, &read, &write, &except, tvp);
+      if (select(FD_SETSIZE, &read, &write, &except, tvp) == -1)
+        errcode = WSAGetLastError();
       leave_blocking_section();
-      if (retcode == -1) {
-	win32_maperr(WSAGetLastError());
+      if (errcode) {
+	win32_maperr(errcode);
 	uerror("select", Nothing);
       }
       read_list = fdset_to_fdlist(readfds, &read);
diff --git a/otherlibs/win32unix/sendrecv.c b/otherlibs/win32unix/sendrecv.c
index 7359feb58..d820f5d0b 100644
--- a/otherlibs/win32unix/sendrecv.c
+++ b/otherlibs/win32unix/sendrecv.c
@@ -31,15 +31,17 @@ CAMLprim value unix_recv(value sock, value buff, value ofs, value len, value fla
   int ret;
   intnat numbytes;
   char iobuf[UNIX_BUFFER_SIZE];
+  DWORD errcode = 0;
 
   Begin_root (buff);
     numbytes = Long_val(len);
     if (numbytes > UNIX_BUFFER_SIZE) numbytes = UNIX_BUFFER_SIZE;
     enter_blocking_section();
     ret = recv(s, iobuf, (int) numbytes, flg);
+    if (ret == -1) errcode = WSAGetLastError();
     leave_blocking_section();
     if (ret == -1) {
-      win32_maperr(WSAGetLastError());
+      win32_maperr(errcode);
       uerror("recv", Nothing);
     }
     memmove (&Byte(buff, Long_val(ofs)), iobuf, ret);
@@ -58,6 +60,7 @@ CAMLprim value unix_recvfrom(value sock, value buff, value ofs, value len, value
   value adr = Val_unit;
   union sock_addr_union addr;
   socklen_param_type addr_len;
+  DWORD errcode = 0;
 
   Begin_roots2 (buff, adr);
     numbytes = Long_val(len);
@@ -65,9 +68,10 @@ CAMLprim value unix_recvfrom(value sock, value buff, value ofs, value len, value
     addr_len = sizeof(sock_addr);
     enter_blocking_section();
     ret = recvfrom(s, iobuf, (int) numbytes, flg, &addr.s_gen, &addr_len);
+    if (ret == -1) errcode = WSAGetLastError();
     leave_blocking_section();
     if (ret == -1) {
-      win32_maperr(WSAGetLastError());
+      win32_maperr(errcode);
       uerror("recvfrom", Nothing);
     }
     memmove (&Byte(buff, Long_val(ofs)), iobuf, ret);
@@ -86,15 +90,17 @@ CAMLprim value unix_send(value sock, value buff, value ofs, value len, value fla
   int ret;
   intnat numbytes;
   char iobuf[UNIX_BUFFER_SIZE];
+  DWORD errcode = 0;
 
   numbytes = Long_val(len);
   if (numbytes > UNIX_BUFFER_SIZE) numbytes = UNIX_BUFFER_SIZE;
   memmove (iobuf, &Byte(buff, Long_val(ofs)), numbytes);
   enter_blocking_section();
   ret = send(s, iobuf, (int) numbytes, flg);
+  if (ret == -1) errcode = WSAGetLastError();
   leave_blocking_section();
   if (ret == -1) {
-    win32_maperr(WSAGetLastError());
+    win32_maperr(errcode);
     uerror("send", Nothing);
   }
   return Val_int(ret);
@@ -109,6 +115,7 @@ value unix_sendto_native(value sock, value buff, value ofs, value len, value fla
   char iobuf[UNIX_BUFFER_SIZE];
   union sock_addr_union addr;
   socklen_param_type addr_len;
+  DWORD errcode = 0;
 
   get_sockaddr(dest, &addr, &addr_len);
   numbytes = Long_val(len);
@@ -116,9 +123,10 @@ value unix_sendto_native(value sock, value buff, value ofs, value len, value fla
   memmove (iobuf, &Byte(buff, Long_val(ofs)), numbytes);
   enter_blocking_section();
   ret = sendto(s, iobuf, (int) numbytes, flg, &addr.s_gen, addr_len);
+  if (ret == -1) errcode = WSAGetLastError();
   leave_blocking_section();
   if (ret == -1) {
-    win32_maperr(WSAGetLastError());
+    win32_maperr(errcode);
     uerror("sendto", Nothing);
   }
   return Val_int(ret);
diff --git a/otherlibs/win32unix/winwait.c b/otherlibs/win32unix/winwait.c
index bac345b40..873c84a5d 100644
--- a/otherlibs/win32unix/winwait.c
+++ b/otherlibs/win32unix/winwait.c
@@ -43,14 +43,16 @@ CAMLprim value win_waitpid(value vflags, value vpid_req)
   int flags;
   DWORD status, retcode;
   HANDLE pid_req = (HANDLE) Long_val(vpid_req);
+  DWORD errcode = 0;
 
   flags = convert_flag_list(vflags, wait_flag_table);
   if ((flags & CAML_WNOHANG) == 0) {
     enter_blocking_section();
     retcode = WaitForSingleObject(pid_req, INFINITE);
+    if (retcode == WAIT_FAILED) errcode = GetLastError();
     leave_blocking_section();
-    if (retcode == WAIT_FAILED) {
-      win32_maperr(GetLastError());
+    if (errcode) {
+      win32_maperr(errcode);
       uerror("waitpid", Nothing);
     }
   }
diff --git a/otherlibs/win32unix/write.c b/otherlibs/win32unix/write.c
index 8c255e11a..284a4755b 100644
--- a/otherlibs/win32unix/write.c
+++ b/otherlibs/win32unix/write.c
@@ -25,6 +25,7 @@ CAMLprim value unix_write(value fd, value buf, value vofs, value vlen)
   intnat ofs, len, written;
   DWORD numbytes, numwritten;
   char iobuf[UNIX_BUFFER_SIZE];
+  DWORD errcode = 0;
 
   Begin_root (buf);
     ofs = Long_val(vofs);
@@ -38,22 +39,19 @@ CAMLprim value unix_write(value fd, value buf, value vofs, value vlen)
         SOCKET s = Socket_val(fd);
         enter_blocking_section();
         ret = send(s, iobuf, numbytes, 0);
+        if (ret == SOCKET_ERROR) errcode = WSAGetLastError();
         leave_blocking_section();
-        if (ret == SOCKET_ERROR) {
-          win32_maperr(WSAGetLastError());
-          uerror("write", Nothing);
-        }
         numwritten = ret;
       } else {
-        BOOL ret;
         HANDLE h = Handle_val(fd);
         enter_blocking_section();
-        ret = WriteFile(h, iobuf, numbytes, &numwritten, NULL);
+        if (! WriteFile(h, iobuf, numbytes, &numwritten, NULL))
+          errcode = GetLastError();
         leave_blocking_section();
-        if (! ret) {
-          win32_maperr(GetLastError());
-          uerror("write", Nothing);
-        }
+      }
+      if (errcode) {
+        win32_maperr(errcode);
+        uerror("write", Nothing);
       }
       written += numwritten;
       ofs += numwritten;
@@ -81,22 +79,19 @@ CAMLprim value unix_single_write(value fd, value buf, value vofs, value vlen)
         SOCKET s = Socket_val(fd);
         enter_blocking_section();
         ret = send(s, iobuf, numbytes, 0);
+        if (ret == SOCKET_ERROR) errcode = WSAGetLastError();
         leave_blocking_section();
-        if (ret == SOCKET_ERROR) {
-          win32_maperr(WSAGetLastError());
-          uerror("single_write", Nothing);
-        }
         numwritten = ret;
       } else {
-        BOOL ret;
         HANDLE h = Handle_val(fd);
         enter_blocking_section();
-        ret = WriteFile(h, iobuf, numbytes, &numwritten, NULL);
+        if (! WriteFile(h, iobuf, numbytes, &numwritten, NULL))
+          errcode = GetLastError();
         leave_blocking_section();
-        if (! ret) {
-          win32_maperr(GetLastError());
-          uerror("single_write", Nothing);
-        }
+      }
+      if (errcode) {
+        win32_maperr(errcode);
+        uerror("single_write", Nothing);
       }
       written = numwritten;
     }