diff --git a/src/microhttpd/test_upgrade.c b/src/microhttpd/test_upgrade.c
index b41a5561..b691bcda 100644
--- a/src/microhttpd/test_upgrade.c
+++ b/src/microhttpd/test_upgrade.c
@@ -569,7 +569,7 @@ make_blocking (MHD_socket fd)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
 #elif defined(MHD_WINSOCK_SOCKETS)
-  unsigned long flags = 1;
+  unsigned long flags = 0;
 
   ioctlsocket (fd, (int) FIONBIO, &flags);
 #endif /* MHD_WINSOCK_SOCKETS */
diff --git a/src/microhttpd/test_upgrade_large.c b/src/microhttpd/test_upgrade_large.c
index 4c54905d..6bbaf04d 100644
--- a/src/microhttpd/test_upgrade_large.c
+++ b/src/microhttpd/test_upgrade_large.c
@@ -743,7 +743,7 @@ make_blocking (MHD_socket fd)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
 #elif defined(MHD_WINSOCK_SOCKETS)
-  unsigned long flags = 1;
+  unsigned long flags = 0;
 
   ioctlsocket (fd, (int) FIONBIO, &flags);
 #endif /* MHD_WINSOCK_SOCKETS */