diff --git a/src/proto_tcp.c b/src/proto_tcp.c
index e744c76..c8f4768 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -233,6 +233,9 @@
  *  - SN_ERR_RESOURCE if a system resource is lacking (eg: fd limits, ports, ...)
  *  - SN_ERR_INTERNAL for any other purely internal errors
  * Additionnally, in the case of SN_ERR_RESOURCE, an emergency log will be emitted.
+ *
+ * The connection's fd is inserted only when SN_ERR_NONE is returned, otherwise
+ * it's invalid and the caller has nothing to do.
  */
 
 int tcp_connect_server(struct connection *conn, int data)