diff --git a/modbus/modbus.c b/modbus/modbus.c
index dd047f1..b031614 100644
--- a/modbus/modbus.c
+++ b/modbus/modbus.c
@@ -1659,7 +1659,8 @@ static int modbus_connect_tcp(modbus_param_t *mb_param)
         return 0;
 }
 
-/* Establishes a modbus connexion */
+/* Establishes a modbus connexion.
+   Returns -1 if an error occured. */
 int modbus_connect(modbus_param_t *mb_param)
 {
         int ret;
diff --git a/modbus/modbus.h b/modbus/modbus.h
index d1f8c21..8a133f1 100644
--- a/modbus/modbus.h
+++ b/modbus/modbus.h
@@ -241,7 +241,8 @@ void modbus_init_tcp(modbus_param_t *mb_param, char *ip_address, int port);
  */
 void modbus_set_error_handling(modbus_param_t *mb_param, error_handling_t error_handling);
 
-/* Establishes a modbus connexion */
+/* Establishes a modbus connexion.
+   Returns -1 if an error occured. */
 int modbus_connect(modbus_param_t *mb_param);
 
 /* Closes a modbus connection */