diff --git a/configure.in b/configure.in
index eff93a08..1ff36b3f 100644
--- a/configure.in
+++ b/configure.in
@@ -82,6 +82,11 @@ AC_ARG_ENABLE(tunemu,
   ]
 )
 
+AC_ARG_WITH(windows2000,
+  AS_HELP_STRING([--with-windows2000], [compile with support for Windows 2000. This disables support for tunneling over existing IPv6 networks.]),
+  [AC_DEFINE(WITH_WINDOWS2000, 1, [Compile with support for Windows 2000])]
+)
+
 AM_CONDITIONAL(TUNEMU, test "$tunemu" = true)
 
 AC_CACHE_SAVE
@@ -143,7 +148,7 @@ AC_CHECK_FUNC(gethostbyname, [], [
   AC_CHECK_LIB(nsl, gethostbyname)
 ])
 
-AC_CHECK_FUNCS([freeaddrinfo gai_strerror getaddrinfo getnameinfo inet_aton],
+AC_CHECK_DECLS([freeaddrinfo, gai_strerror, getaddrinfo, getnameinfo],
   [], [], [#include "have.h"]
 )
 
diff --git a/have.h b/have.h
index 8a58af33..7e2930dc 100644
--- a/have.h
+++ b/have.h
@@ -31,6 +31,17 @@
 #include <fcntl.h>
 #include <unistd.h>
 
+#ifdef HAVE_MINGW
+#ifdef WITH_WINDOWS2000
+#define WINVER Windows2000
+#else
+#define WINVER WindowsXP
+#endif
+#include <w32api.h>
+#include <windows.h>
+#include <ws2tcpip.h>
+#endif
+
 #ifdef HAVE_STDBOOL_H
 #include <stdbool.h>
 #endif
@@ -160,9 +171,4 @@
 #include <netinet/if_ether.h>
 #endif
 
-#ifdef HAVE_MINGW
-#include <windows.h>
-#include <winsock2.h>
-#endif
-
 #endif /* __TINC_SYSTEM_H__ */
diff --git a/lib/dropin.h b/lib/dropin.h
index 72109c84..4db7d7e0 100644
--- a/lib/dropin.h
+++ b/lib/dropin.h
@@ -39,11 +39,6 @@ extern int asprintf(char **, const char *, ...);
 extern int vasprintf(char **, const char *, va_list ap);
 #endif
 
-#ifndef HAVE_GETNAMEINFO
-extern int getnameinfo(const struct sockaddr *sa, size_t salen, char *host,
-					   size_t hostlen, char *serv, size_t servlen, int flags);
-#endif
-
 #ifndef HAVE_GETTIMEOFDAY
 extern int gettimeofday(struct timeval *, void *);
 #endif
diff --git a/lib/fake-getaddrinfo.c b/lib/fake-getaddrinfo.c
index 14420b58..10672b7e 100644
--- a/lib/fake-getaddrinfo.c
+++ b/lib/fake-getaddrinfo.c
@@ -16,7 +16,7 @@
 #include "fake-getaddrinfo.h"
 #include "xalloc.h"
 
-#ifndef HAVE_GAI_STRERROR
+#if !HAVE_DECL_GAI_STRERROR
 char *gai_strerror(int ecode)
 {
 	switch (ecode) {
@@ -32,7 +32,7 @@ char *gai_strerror(int ecode)
 }    
 #endif /* !HAVE_GAI_STRERROR */
 
-#ifndef HAVE_FREEADDRINFO
+#if !HAVE_DECL_FREEADDRINFO
 void freeaddrinfo(struct addrinfo *ai)
 {
 	struct addrinfo *next;
@@ -45,7 +45,7 @@ void freeaddrinfo(struct addrinfo *ai)
 }
 #endif /* !HAVE_FREEADDRINFO */
 
-#ifndef HAVE_GETADDRINFO
+#if !HAVE_DECL_GETADDRINFO
 static struct addrinfo *malloc_ai(uint16_t port, uint32_t addr)
 {
 	struct addrinfo *ai;
diff --git a/lib/fake-getaddrinfo.h b/lib/fake-getaddrinfo.h
index d2b46f62..d31a89a1 100644
--- a/lib/fake-getaddrinfo.h
+++ b/lib/fake-getaddrinfo.h
@@ -33,16 +33,16 @@ struct addrinfo {
 };
 #endif /* !HAVE_STRUCT_ADDRINFO */
 
-#ifndef HAVE_GETADDRINFO
+#if !HAVE_DECL_GETADDRINFO
 int getaddrinfo(const char *hostname, const char *servname, 
                 const struct addrinfo *hints, struct addrinfo **res);
 #endif /* !HAVE_GETADDRINFO */
 
-#ifndef HAVE_GAI_STRERROR
+#if !HAVE_DECL_GAI_STRERROR
 char *gai_strerror(int ecode);
 #endif /* !HAVE_GAI_STRERROR */
 
-#ifndef HAVE_FREEADDRINFO
+#if !HAVE_DECL_FREEADDRINFO
 void freeaddrinfo(struct addrinfo *ai);
 #endif /* !HAVE_FREEADDRINFO */
 
diff --git a/lib/fake-getnameinfo.c b/lib/fake-getnameinfo.c
index 796efdf8..80471730 100644
--- a/lib/fake-getnameinfo.c
+++ b/lib/fake-getnameinfo.c
@@ -14,7 +14,7 @@
 #include "fake-getnameinfo.h"
 #include "fake-getaddrinfo.h"
 
-#ifndef HAVE_GETNAMEINFO
+#if !HAVE_DECL_GETNAMEINFO
 
 int getnameinfo(const struct sockaddr *sa, size_t salen, char *host, size_t hostlen, char *serv, size_t servlen, int flags)
 {
diff --git a/lib/fake-getnameinfo.h b/lib/fake-getnameinfo.h
index 0f0b4bcc..02ac77a1 100644
--- a/lib/fake-getnameinfo.h
+++ b/lib/fake-getnameinfo.h
@@ -3,7 +3,7 @@
 #ifndef _FAKE_GETNAMEINFO_H
 #define _FAKE_GETNAMEINFO_H
 
-#ifndef HAVE_GETNAMEINFO
+#if !HAVE_DECL_GETNAMEINFO
 int getnameinfo(const struct sockaddr *sa, size_t salen, char *host, 
                 size_t hostlen, char *serv, size_t servlen, int flags);
 #endif /* !HAVE_GETNAMEINFO */