diff --git a/changes/bug5861 b/changes/bug5861
new file mode 100644
index 0000000000..74a1dfb95f
--- /dev/null
+++ b/changes/bug5861
@@ -0,0 +1,4 @@
+  o Minor bugfixes:
+    - Set _WIN32_WINNT to 0x0501 consistently throughout the code, so
+      that IPv6 stuff will compile on MSVC, and compilation issues
+      will be easier to track down. Fix for bug 5861.
diff --git a/configure.in b/configure.in
index f4e0fea704..43c9bb2a5e 100644
--- a/configure.in
+++ b/configure.in
@@ -796,8 +796,7 @@ AC_CHECK_TYPES([struct in6_addr, struct sockaddr_in6, sa_family_t], , ,
 #include <sys/socket.h>
 #endif
 #ifdef _WIN32
-#define WIN32_WINNT 0x400
-#define _WIN32_WINNT 0x400
+#define _WIN32_WINNT 0x0501
 #define WIN32_LEAN_AND_MEAN
 #if defined(_MSC_VER) && (_MSC_VER < 1300)
 #include <winsock.h>
@@ -821,8 +820,7 @@ AC_CHECK_MEMBERS([struct in6_addr.s6_addr32, struct in6_addr.s6_addr16, struct s
 #include <sys/socket.h>
 #endif
 #ifdef _WIN32
-#define WIN32_WINNT 0x400
-#define _WIN32_WINNT 0x400
+#define _WIN32_WINNT 0x0501
 #define WIN32_LEAN_AND_MEAN
 #if defined(_MSC_VER) && (_MSC_VER < 1300)
 #include <winsock.h>
diff --git a/src/common/aes.c b/src/common/aes.c
index a9a018851b..1cb6b86a82 100644
--- a/src/common/aes.c
+++ b/src/common/aes.c
@@ -12,11 +12,8 @@
 #include "orconfig.h"
 
 #ifdef _WIN32 /*wrkard for dtls1.h >= 0.9.8m of "#include <winsock.h>"*/
- #ifndef WIN32_WINNT
- #define WIN32_WINNT 0x400
- #endif
  #ifndef _WIN32_WINNT
- #define _WIN32_WINNT 0x400
+ #define _WIN32_WINNT 0x0501
  #endif
  #define WIN32_LEAN_AND_MEAN
  #if defined(_MSC_VER) && (_MSC_VER < 1300)
diff --git a/src/common/compat.h b/src/common/compat.h
index 65e6cb49e0..b0ef63badf 100644
--- a/src/common/compat.h
+++ b/src/common/compat.h
@@ -9,11 +9,8 @@
 #include "orconfig.h"
 #include "torint.h"
 #ifdef _WIN32
-#ifndef WIN32_WINNT
-#define WIN32_WINNT 0x400
-#endif
 #ifndef _WIN32_WINNT
-#define _WIN32_WINNT 0x400
+#define _WIN32_WINNT 0x0501
 #endif
 #define WIN32_LEAN_AND_MEAN
 #if defined(_MSC_VER) && (_MSC_VER < 1300)
diff --git a/src/common/crypto.c b/src/common/crypto.c
index e37b282757..f82598fab2 100644
--- a/src/common/crypto.c
+++ b/src/common/crypto.c
@@ -13,11 +13,8 @@
 #include "orconfig.h"
 
 #ifdef _WIN32
-#ifndef WIN32_WINNT
-#define WIN32_WINNT 0x400
-#endif
 #ifndef _WIN32_WINNT
-#define _WIN32_WINNT 0x400
+#define _WIN32_WINNT 0x0501
 #endif
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
diff --git a/src/common/tortls.c b/src/common/tortls.c
index 12d982defb..1120f3e8be 100644
--- a/src/common/tortls.c
+++ b/src/common/tortls.c
@@ -22,11 +22,8 @@
 
 #include <assert.h>
 #ifdef _WIN32 /*wrkard for dtls1.h >= 0.9.8m of "#include <winsock.h>"*/
- #ifndef WIN32_WINNT
- #define WIN32_WINNT 0x400
- #endif
  #ifndef _WIN32_WINNT
- #define _WIN32_WINNT 0x400
+ #define _WIN32_WINNT 0x0501
  #endif
  #define WIN32_LEAN_AND_MEAN
  #if defined(_MSC_VER) && (_MSC_VER < 1300)
diff --git a/src/or/or.h b/src/or/or.h
index b8fee649ea..76681c9eea 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -23,11 +23,8 @@
 #endif
 
 #ifdef _WIN32
-#ifndef WIN32_WINNT
-#define WIN32_WINNT 0x400
-#endif
 #ifndef _WIN32_WINNT
-#define _WIN32_WINNT 0x400
+#define _WIN32_WINNT 0x0501
 #endif
 #define WIN32_LEAN_AND_MEAN
 #endif