diff --git a/src/prototcp.c b/src/prototcp.c
index 930fbd3..0d72412 100644
--- a/src/prototcp.c
+++ b/src/prototcp.c
@@ -93,7 +93,8 @@ prototcp_bufferevent_free_and_close_fd(struct bufferevent *bev, UNUSED pxy_conn_
 	log_finer_va("in=%zu, out=%zu, fd=%d", evbuffer_get_length(bufferevent_get_input(bev)), evbuffer_get_length(bufferevent_get_output(bev)), fd);
 
 	bufferevent_free(bev);
-	evutil_closesocket(fd);
+	if (fd >= 0)
+		evutil_closesocket(fd);
 }
 
 int