diff --git a/ext/sockets/sockets.c b/ext/sockets/sockets.c
index 8398e004d0b6c..ea3d82118451a 100644
--- a/ext/sockets/sockets.c
+++ b/ext/sockets/sockets.c
@@ -553,6 +553,9 @@ static PHP_MINIT_FUNCTION(sockets)
 #ifdef TCP_NODELAY
 	REGISTER_LONG_CONSTANT("TCP_NODELAY",   TCP_NODELAY,    CONST_CS | CONST_PERSISTENT);
 #endif
+#ifdef TCP_NOTSENT_LOWAT
+	REGISTER_LONG_CONSTANT("TCP_NOTSENT_LOWAT",  TCP_NOTSENT_LOWAT,   CONST_CS | CONST_PERSISTENT);
+#endif
 #ifdef TCP_DEFER_ACCEPT
 	REGISTER_LONG_CONSTANT("TCP_DEFER_ACCEPT",   TCP_DEFER_ACCEPT,    CONST_CS | CONST_PERSISTENT);
 #endif