Index: libmicrohttpd-0.9.76/src/microhttpd/connection.c
===================================================================
--- libmicrohttpd-0.9.76.orig/src/microhttpd/connection.c
+++ libmicrohttpd-0.9.76/src/microhttpd/connection.c
@@ -1612,8 +1612,6 @@ connection_maximize_write_buffer (struct
   return c->write_buffer_size - c->write_buffer_append_offset;
 }
 
-
-#if 0 /* disable unused function */
 /**
  * Shrink connection write buffer to the size of unsent data.
  *
@@ -1654,10 +1652,6 @@ connection_shrink_write_buffer (struct M
     c->write_buffer = new_buf;
 }
 
-
-#endif /* unused function */
-
-
 /**
  * Switch connection from recv mode to send mode.
  *
@@ -4700,6 +4694,8 @@ MHD_connection_handle_idle (struct MHD_C
 #ifdef UPGRADE_SUPPORT
       if (NULL != connection->response->upgrade_handler)
       {
+        connection_shrink_write_buffer(connection);
+
         connection->state = MHD_CONNECTION_UPGRADE;
         /* This connection is "upgraded".  Pass socket to application. */
         if (MHD_NO ==