Index: libmicrohttpd-0.4.6/src/daemon/daemon.c
===================================================================
--- libmicrohttpd-0.4.6.orig/src/daemon/daemon.c	2010-02-20 10:00:01.000000000 +0100
+++ libmicrohttpd-0.4.6/src/daemon/daemon.c	2012-01-15 16:30:54.000000000 +0100
@@ -695,6 +695,25 @@
     }
 #endif
 
+#if HAVE_INET6
+    /* If receiving IPv4 connections on an IPv6 socket (dual-stack sockets),
+     * the operating system will typically report back a so called mapped-v4
+     * address, of the form ::ffff:127.0.0.1. Rewrite these to IPv4 addresses,
+     * since that is what all the other code expects.
+     */
+    if (addrstorage.sin6_family == AF_INET6) {
+      const uint32_t *addr32 = (const uint32_t *) addrstorage.sin6_addr.s6_addr;
+      if (addr32[0] == 0 && addr32[1] == 0 && addr32[2] == htonl(0xffff)) {
+        uint32_t addr4 = addr32[3];
+        uint16_t port = addrstorage.sin6_port;
+
+        struct sockaddr_in *addr_in = (struct sockaddr_in *) &addrstorage;
+        addr_in->sin_family = AF_INET;
+        addr_in->sin_addr.s_addr = addr4;
+        addr_in->sin_port = port;
+      }
+    } 
+#endif
 
 #if HAVE_MESSAGES
 #if DEBUG_CONNECT
@@ -1411,6 +1430,7 @@
                      void *apc_cls,
                      MHD_AccessHandlerCallback dh, void *dh_cls, va_list ap)
 {
+  const int off = 0;
   const int on = 1;
   struct MHD_Daemon *retVal;
   int socket_fd;
@@ -1507,20 +1527,57 @@
       return NULL;
     }
 #endif
-  if ((options & MHD_USE_IPv6) != 0)
-#if HAVE_INET6
-    socket_fd = SOCKET (PF_INET6, SOCK_STREAM, 0);
-#else
+
+  /* MHD_USE_DUALSTACK overrides MHD_USE_IPv6. */
+  if ((options & MHD_USE_DUALSTACK) != 0)
+    options &= ~MHD_USE_IPv6;
+
+#if HAVE_INET6 && defined(IPV6_V6ONLY)
+  /* If we have IPv6 support, and support the IPV6_V6ONLY flag from
+   * RFC3493, we can support IPv4 and IPv6 on the same socket.
+   * If not, we ignore the flag and open it as IPv4-only.
+   */
+  if ((options & MHD_USE_DUALSTACK) != 0)
     {
+      socket_fd = SOCKET (PF_INET6, SOCK_STREAM, 0);
+      if (socket_fd == -1)
+        {
+          options &= ~MHD_USE_DUALSTACK;
+        }
+      else if (SETSOCKOPT (socket_fd,
+                           IPPROTO_IPV6,
+                           IPV6_V6ONLY,
+                           &off, sizeof (off)) < 0)
+        {
 #if HAVE_MESSAGES
-      fprintf (stderr, "AF_INET6 not supported\n");
+          FPRINTF (stderr, "setsockopt(IPV6_V6ONLY) failed: %s\n", STRERROR (errno));
 #endif
-      free (retVal);
-      return NULL;
+          CLOSE (socket_fd);
+          options &= ~MHD_USE_DUALSTACK;
+        }
     }
 #endif
-  else
-    socket_fd = SOCKET (PF_INET, SOCK_STREAM, 0);
+
+  /* If MHD_USE_DUALSTACK is set at this point, we have a working socket
+   * and should not try to create a new one. Otherwise, open one here.
+   */
+  if ((options & MHD_USE_DUALSTACK) == 0)
+    {
+      if ((options & MHD_USE_IPv6) != 0)
+#if HAVE_INET6
+        socket_fd = SOCKET (PF_INET6, SOCK_STREAM, 0);
+#else
+        {
+#if HAVE_MESSAGES
+          fprintf (stderr, "AF_INET6 not supported\n");
+#endif
+          free (retVal);
+          return NULL;
+        }
+#endif
+      else
+        socket_fd = SOCKET (PF_INET, SOCK_STREAM, 0);
+  }
   if (socket_fd == -1)
     {
 #if HAVE_MESSAGES
@@ -1566,7 +1623,7 @@
   if (NULL == servaddr)
     {
 #if HAVE_INET6
-      if ((options & MHD_USE_IPv6) != 0)
+      if ((options & MHD_USE_IPv6) != 0 || (options & MHD_USE_DUALSTACK) != 0)
         {
           memset (&servaddr6, 0, sizeof (struct sockaddr_in6));
           servaddr6.sin6_family = AF_INET6;
Index: libmicrohttpd-0.4.6/src/include/microhttpd.h
===================================================================
--- libmicrohttpd-0.4.6.orig/src/include/microhttpd.h	2010-03-13 09:41:30.000000000 +0100
+++ libmicrohttpd-0.4.6/src/include/microhttpd.h	2012-01-15 14:54:00.000000000 +0100
@@ -299,7 +299,14 @@
    * This option only works in conjunction with MHD_USE_THREAD_PER_CONNECTION
    * (at this point).
    */
-  MHD_USE_POLL = 64
+  MHD_USE_POLL = 64,
+
+  /**
+   * Accept both IPv6 and IPv4 connections if possible; otherwise,
+   * fall back to IPv4. Will override MHD_USE_IPv6, so if you give this flag,
+   * you will never get a pure IPv6 socket.
+   */
+  MHD_USE_DUALSTACK = 128,
 };
 
 /**