diff --git a/include/types/connection.h b/include/types/connection.h
index 5af651f..7256219 100644
--- a/include/types/connection.h
+++ b/include/types/connection.h
@@ -259,6 +259,7 @@
 enum {
 	CO_RFL_BUF_WET     = 0x0001,    /* Buffer still has some output data present */
 	CO_RFL_BUF_FLUSH   = 0x0002,    /* Flush mux's buffers but don't read more data */
+	CO_RFL_KEEP_RSV    = 0x0004,    /* Don't fill the reserved space */
 };
 
 /* flags that can be passed to xprt->snd_buf() and mux->snd_buf() */