diff --git a/BUILDING b/BUILDING
index 87e23c643..830f58b21 100644
--- a/BUILDING
+++ b/BUILDING
@@ -14,8 +14,8 @@ Build Prerequisites:
   * On Windows only, Yasm[4] is required.
 
   * A C compiler is required. On Windows, MSVC 12 (Visual Studio 2013) or later
-    are supported. Recent versions of GCC and Clang should work on non-Windows
-    platforms, and maybe on Windows too.
+    with Platform SDK 8.1 or later are supported. Recent versions of GCC and
+    Clang should work on non-Windows platforms, and maybe on Windows too.
 
   * Bash is required for running some tests, but not for building.
 
diff --git a/crypto/bio/bio_test.c b/crypto/bio/bio_test.c
index db6fc026e..57684df54 100644
--- a/crypto/bio/bio_test.c
+++ b/crypto/bio/bio_test.c
@@ -26,6 +26,7 @@
 #include <sys/socket.h>
 #include <unistd.h>
 #else
+#define WIN32_LEAN_AND_MEAN
 #include <io.h>
 #include <WinSock2.h>
 #include <WS2tcpip.h>
diff --git a/crypto/bio/connect.c b/crypto/bio/connect.c
index 9bd87d4f9..55b9352aa 100644
--- a/crypto/bio/connect.c
+++ b/crypto/bio/connect.c
@@ -65,6 +65,10 @@
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <unistd.h>
+#else
+#define WIN32_LEAN_AND_MEAN
+#include <WinSock2.h>
+#include <WS2tcpip.h>
 #endif
 
 #include <openssl/buf.h>
diff --git a/crypto/bio/fd.c b/crypto/bio/fd.c
index bc47e746f..c5133d805 100644
--- a/crypto/bio/fd.c
+++ b/crypto/bio/fd.c
@@ -61,6 +61,7 @@
 #if !defined(OPENSSL_WINDOWS)
 #include <unistd.h>
 #else
+#define WIN32_LEAN_AND_MEAN
 #include <io.h>
 #include <Windows.h>
 #endif
diff --git a/crypto/bio/internal.h b/crypto/bio/internal.h
index ba28839ac..d9a34f18e 100644
--- a/crypto/bio/internal.h
+++ b/crypto/bio/internal.h
@@ -67,8 +67,7 @@ typedef unsigned short u_short;
 #include <sys/types.h>
 #include <sys/socket.h>
 #else
-#include <WinSock2.h>
-#include <WS2tcpip.h>
+typedef int socklen_t;
 #endif
 
 #if defined(__cplusplus)
diff --git a/crypto/bio/socket.c b/crypto/bio/socket.c
index 90ae14a6d..6d393a22e 100644
--- a/crypto/bio/socket.c
+++ b/crypto/bio/socket.c
@@ -61,6 +61,9 @@
 
 #if !defined(OPENSSL_WINDOWS)
 #include <unistd.h>
+#else
+#define WIN32_LEAN_AND_MEAN
+#include <WinSock2.h>
 #endif
 
 #include "internal.h"
diff --git a/crypto/bio/socket_helper.c b/crypto/bio/socket_helper.c
index ba65a1a43..801800a55 100644
--- a/crypto/bio/socket_helper.c
+++ b/crypto/bio/socket_helper.c
@@ -24,9 +24,9 @@
 #include <netdb.h>
 #include <unistd.h>
 #else
+#define WIN32_LEAN_AND_MEAN
 #include <WinSock2.h>
 #include <WS2tcpip.h>
-typedef int socklen_t;
 #endif
 
 #include "internal.h"
diff --git a/crypto/directory_win.c b/crypto/directory_win.c
index 4956383db..203d4a202 100644
--- a/crypto/directory_win.c
+++ b/crypto/directory_win.c
@@ -30,6 +30,7 @@
 
 #if defined(OPENSSL_WINDOWS)
 
+#define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 #include <tchar.h>
 #include <errno.h>
diff --git a/crypto/err/err.c b/crypto/err/err.c
index 892b2ac83..5ee81ca81 100644
--- a/crypto/err/err.c
+++ b/crypto/err/err.c
@@ -115,6 +115,7 @@
 #include <stdio.h>
 
 #if defined(OPENSSL_WINDOWS)
+#define WIN32_LEAN_AND_MEAN
 #include <Windows.h>
 #endif
 
diff --git a/crypto/mem.c b/crypto/mem.c
index 11ef33524..834141173 100644
--- a/crypto/mem.c
+++ b/crypto/mem.c
@@ -65,6 +65,7 @@
 #include <string.h>
 
 #if defined(OPENSSL_WINDOWS)
+#define WIN32_LEAN_AND_MEAN
 #include <Windows.h>
 #else
 #include <strings.h>
diff --git a/crypto/rand/windows.c b/crypto/rand/windows.c
index ed6e5e9ed..86bea8584 100644
--- a/crypto/rand/windows.c
+++ b/crypto/rand/windows.c
@@ -16,6 +16,7 @@
 
 #if defined(OPENSSL_WINDOWS)
 
+#define WIN32_LEAN_AND_MEAN
 #include <limits.h>
 #include <stdlib.h>
 #include <Windows.h>
diff --git a/crypto/thread.c b/crypto/thread.c
index 15e38bdd2..b1b4d00ef 100644
--- a/crypto/thread.c
+++ b/crypto/thread.c
@@ -59,6 +59,7 @@
 #include <errno.h>
 
 #if defined(OPENSSL_WINDOWS)
+#define WIN32_LEAN_AND_MEAN
 #include <Windows.h>
 #endif
 
diff --git a/tool/speed.cc b/tool/speed.cc
index cfffcb05b..8184339ef 100644
--- a/tool/speed.cc
+++ b/tool/speed.cc
@@ -27,6 +27,7 @@
 #include <openssl/rsa.h>
 
 #if defined(OPENSSL_WINDOWS)
+#define WIN32_LEAN_AND_MEAN
 #include <Windows.h>
 #elif defined(OPENSSL_APPLE)
 #include <sys/time.h>
diff --git a/tool/transport_common.cc b/tool/transport_common.cc
index c2b3e0c83..00b4a8b52 100644
--- a/tool/transport_common.cc
+++ b/tool/transport_common.cc
@@ -35,7 +35,6 @@
 #include <io.h>
 #include <WinSock2.h>
 #include <WS2tcpip.h>
-typedef int socklen_t;
 typedef int ssize_t;
 #define read _read
 #define write _write